Remove Mac related leftovers

The engine doesn't support that platform anyways.

linux/.gitignore

@@ -1,17 +1,12 @@
 # Don't commit compiled mod libraries
 *.so
 *.so.*
-*.dylib
 *.o
 *_map.txt
 
 # Allow Half-Life-specific files that would otherwise be ignored
-!libSDL2.dylib
 !libSDL2.so
-!libSDL2-2.0.0.dylib
-!libSDL2-2.0.0.dylib.dSYM/Contents/Resources/DWARF/libsdl2-2.0.0.dylib
 !libSDL2-2.0.so.0
 !libSDL2-2.0.so.0.dbg
 !vgui.so
-!release/vgui.dylib
 !release/vgui.so