MIPS: Delete unused code in linux32.c

The A() & AA() macros have been unused since commit 05e43966
("[MIPS] Use SYSVIPC_COMPAT to fix various problems on N32"), which
switched to the more standard compat_ptr().

RLIM_INFINITY32, RESOURCE32() & struct rlimit32 have been present but
unused since the beginning of the git era.

Remove the dead code.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20108/
Cc: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org