Remove AltiVec vector declaration compiler compatibility macros.

Remove AltiVec vector declaration compiler compatibility macros.
The original problem was that FSF and Apple gcc used a different syntax
for vector declarations, i.e. {} vs. (). Nowadays Apple gcc versions support
the standard {} syntax and versions that support {} are available on all
relevant Mac OS X versions. Thus the greater compatibility is no longer
worth cluttering the code with macros.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@14366 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b