audio/grip: No longer cater to GCC 4.2

Remove code catering to GCC 4.2 (as system compiler) which is not
necessary any longer sincer USES=compiler and USE_GCC never will
pull that in any more.

This reverts much of commit 2d32b6c73c040e43af60ab5c05912e333704cea
from 3+ years ago.

Approved by: maintainer