Remove _flush_cache(2) for mips64.

Also remove declaration.

The only user is compiler-rt, and they can replace that call with one to
syscall(2). compiler-rt doesn't currently build on mips64 anyway.

Bug: 11156955
Change-Id: Ieae0ba49c8e7aa50253401fc1d7c2d17bc867d39
3 files changed