Re-enable MMX after reports it works on 10.5 and 10.6

Much of the FFmpeg code needs precise compiler/assembler/linker settings
to build cleanly with some of Apple's GCC versions. We used to have to
disable MMX because we used our own settings to build everything.
After switching to using the FFmpeg Makefile, it builds cleanly again.

Author: NigelPearson

OSX/build/osx-packager.pl

@@ -546,9 +546,6 @@ END
         # To "cross compile" something for a lesser Mac:
         #'--tune=G3',
         #'--disable-altivec',
-
-        # Currently needed for Mac OS 10.6 builds?
-        '--disable-mmx', '--enable-disable-mmx-for-debugging',
       ],
 );