MIPS: remove GCC < 4.9 support

Remove a tautology; since
commit 0bddd227 ("Documentation: update for gcc 4.9 requirement")
which raised the minimally supported version of GCC to 4.9, this case is
always true.

Link: https://github.com/ClangBuiltLinux/linux/issues/427


Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>