MIPS: VDSO: Remove unused gettimeofday.c

arch/mips/vdso/gettimeofday.c has been unused since commit 24640f23
("mips: Add support for generic vDSO"). Remove the dead code.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: 24640f23 ("mips: Add support for generic vDSO")
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: linux-mips@vger.kernel.org