Remove patch-gcc-gengtype-fix.diff

During the toolchain refresh the action of this patch was
reversed so that instead of *fixing* a bug in gcc-4.6 it instead
introduces a bug into gcc-4.7. This patch is not required with
the latest versions of gcc.

--- additional info ---
I don't know if you remember but the gengtype patch corrected a latent bug in the gcc-4.6 sources that was only discovered when the more aggressive optimizer of gcc-4.7 was used to build it. Thus gcc-4.7 already includes the fix *and* reversing the patch prevents the ARM compiler being built if the *host* compiler is gcc-4.7 or later.