drop lilypond pre 2.25.8 compatibility, cause its not working anyway

all_base_includes.ly

@@ -1,11 +1,8 @@
-\include #(if (< (list-ref (ly:version) 1) 24) "legacy-lilypond-compatibility.ly" "void.ly")
-
 #(define noStandaloneOutput (if (defined? 'noStandaloneOutput) noStandaloneOutput #f))
 
 #(if (defined? 'LAYOUT) #f (load "json_parser.scm"))
 #(use-modules (json parser))
 \include "basic_format_and_style_settings.ly"
-\include #(if (< (list-ref (ly:version) 1) 25) "legacy-lilypond-compatibility-pre-2.25.ly" "void.ly")
 \include "eps_file_from_song_dir.ly"
 \include "title_with_category_images.ly"
 \include "auto_rest_merging.ly"

book_include.ly

@@ -1,5 +1,3 @@
-\version "2.18"
-
 #(define song-list '())
 
 #(define (files-in-directory dirname)
@@ -120,7 +118,7 @@ includeSong =
      #{
      \bookOutputName #filename
      #}
-    (ly:parser-parse-string (if (< (list-ref (ly:version) 1) 19) (ly:parser-clone parser) (ly:parser-clone))
+    (ly:parser-parse-string (ly:parser-clone)
       (ly:format "\\include \"~a/~a/~a.ly\"" songPath filename filename))
     (let ((label (gensym "index")))
       (set! additional-page-switch-label-list
@@ -155,7 +153,7 @@ imagepage =
 songs =
 #(define-void-function (parser location) ()
  (for-each (lambda (songitems)
-   (ly:book-add-bookpart! (if (< (list-ref (ly:version) 1) 19) (ly:parser-lookup parser '$current-book) (ly:parser-lookup '$current-book))
+   (ly:book-add-bookpart! (ly:parser-lookup '$current-book)
     (let ((filename (car songitems))
           (songvars (cdr songitems)))
       (if (eq? filename 'emptyPage)

chord_settings.ly

@@ -99,12 +99,10 @@ generalLayout = \layout {
    (interpret-markup layout props
      #{ \markup { \override #'(baseline-skip . 2)
           \center-column {
-            \score { \new ChordNames { #(if (< (list-ref (ly:version) 1) 19)
-              (ly:parser-include-string parser (string-append "\\chordmode { s4 " chord " }"))
-              (ly:parser-include-string (string-append "\\chordmode { s4 " chord " }"))
-              ) } \layout { \generalLayout } }
-            \override #'(fret-diagram-details . (
-                     (barre-type . straight))) {
+            \score { \new ChordNames {
+              #(ly:parser-include-string (string-append "\\chordmode { s4 " chord " }"))
+            } \layout { \generalLayout } }
+            \override #'(fret-diagram-details . ((barre-type . straight))) {
               \fret-diagram-terse #fret
             }
           }

general_include.ly

@@ -1,3 +1,4 @@
+\version "2.25.8"
 #(ly:set-option 'relative-includes #t)
 
 #(define noDefaultOutput #t)

legacy-lilypond-compatibility-pre-2.25.ly

@@ -1,22 +0,0 @@
-% guile regular expressions aktivieren:
-#(use-modules (ice-9 regex))
-
-#(define ly:make-regex make-regexp)
-#(define ly:regex-exec regexp-exec)
-#(define ly:regex-match-substring match:substring)
-#(define (ly:regex-replace pattern text . replacements)
-  (apply regexp-substitute/global #f pattern text 'pre (append replacements (list 'post))))
-
-
-% old font handling
-
-#(define (default-pango size)
-  (make-pango-font-tree
-    songChordFont
-    songLyricFont
-    "Luxi Mono"
-    (/ size 20)))
-
-\paper {
-  #(define fonts (default-pango globalSize))
-}

legacy-lilypond-compatibility.ly

@@ -1,27 +0,0 @@
-% this is to be compatible to older lilypond versions
-\version "2.18.0"
-
-#(define (on-first-page layout props)
-  "Whether the markup is printed on the first page of the book."
-  (= (chain-assoc-get 'page:page-number props -1)
-     (book-first-page layout props)))
-
-#(define-markup-command (if layout props condition? argument)
-  (procedure? markup?)
-  #:category conditionals
-  (if (condition? layout props)
-      (interpret-markup layout props argument)
-      empty-stencil))
-
-#(define (on-first-page-of-part layout props)
-  "Whether the markup is printed on the first page of the book part."
-  (= (chain-assoc-get 'page:page-number props -1)
-     (ly:output-def-lookup layout 'first-page-number)))
-
-#(define (should-print-page-number layout props)
-  "Whether the page number should be printed on this page.  This depends
-on the settings @code{print-@/page-@/numbers} and
-@code{print-@/first-@/page-@/number} of the @code{\\paper} block."
-  (and (eq? #t (ly:output-def-lookup layout 'print-page-number))
-       (or (not (on-first-page layout props))
-           (eq? #t (ly:output-def-lookup layout 'print-first-page-number)))))

title_with_category_images.ly

@@ -35,10 +35,7 @@
            (string-tokenize (chain-assoc-get 'header:categories props ""))))
        (make-null-markup))))
 
-#(define pdf-encode
-   (if (< (list-ref (ly:version) 1) 24)
-       ly:encode-string-for-pdf
-   (@@ (lily framework-ps) pdf-encode)))
+#(define pdf-encode (@@ (lily framework-ps) pdf-encode))
 % PDF tags
 #(define-markup-command (title-to-pdf-toc layout props title) (string?)
      (ly:make-stencil