Fix Number of Measures/System

It got removed because it caused more probelms than it fixed. Just use https://musescore.org/en/handbook/tools#line-breaks, or https://musescore.org/en/handbook/breaks-and-spacers, possibly in combination with https://musescore.org/en/handbook/layout-and-formatting#layout-stretch

To be clear: that feature never actually *fixed* the number of measures; it simply set an upper limit. That is, it would not force MuseScore to fit *more* measures on a system than your current size and spacing settings would allow. It would only force MuseScore to put *fewer* measures on a aystem than it otherwise could. So n that sense, it was no different from adding line breaks, really, but it also had the disadvantage of being extremely inflexible. There was no way to apply this to only a portion of a score, or to have a different number of measures per line on one page versus another, or to control how pickup measures or voltas were counted, etc.

That is why this flawed feature was removed and removed with the far more flexible and powerful tool in Edit / Tools / Add/Remvoe Line Breaks. It solves the aforementioned problems by allowing you to specify the range of measures you would like to apply this to rather than forcing a one-size-fits-all approach.