zrythm: fix build with meson 0.60

Feature flags were renamed in https://github.com/zrythm/zrythm/commit/2f6ca072f09d14993d60e29f4d5c3fbf5a08be02
and the ffmpeg dependency was dropped in https://github.com/zrythm/zrythm/commit/116b9553913a4616599d259fbe22bc30ffe1ed43

pkgs/applications/audio/zrythm/default.nix

@@ -13,7 +13,6 @@
 , curl
 , dconf
 , libepoxy
-, ffmpeg
 , fftw
 , fftwFloat
 , flex
@@ -95,7 +94,6 @@ stdenv.mkDerivation rec {
     curl
     dconf
     libepoxy
-    ffmpeg
     fftw
     fftwFloat
     flex
@@ -133,10 +131,9 @@ stdenv.mkDerivation rec {
   ];
 
   mesonFlags = [
-    "-Denable_ffmpeg=true"
-    "-Denable_rtmidi=true"
-    "-Denable_rtaudio=true"
-    "-Denable_sdl=true"
+    "-Drtmidi=enabled"
+    "-Drtaudio=enabled"
+    "-Dsdl=enabled"
     "-Dcarla=enabled"
     "-Dmanpage=true"
     # "-Duser_manual=true" # needs sphinx-intl