Use \tempo command for midi speed

* Remove Metronome mark engraver
* Remove midiQuarterNoteSpeed

public_includes/layout_bottom.ily

@@ -1,6 +1,3 @@
-% set the speed of the midi music
-#(define midiQuarterNoteSpeed (if (defined? 'midiQuarterNoteSpeed) midiQuarterNoteSpeed 90))
-
 MUSIC = { \transposable #TRANSPOSITION \MUSIC }
 
 verselayout = \layout {
@@ -70,11 +67,6 @@ TEXT = \markuplist {
     \score {
       \unfoldRepeats { \MUSIC \INLINESCOREMUSIC }
       \midi {
-        \context {
-          \Score
-          % Tempo des midi files
-          tempoWholesPerMinute = #(/ midiQuarterNoteSpeed 4)
-        }
         \context {
           \Staff
           \remove "Staff_performer"