ARC: mm: drop stale define of __ARCH_USE_5LEVEL_HACK

Commit 6aae3425 ("ARC: mm: remove __ARCH_USE_5LEVEL_HACK") make ARC
paging code 5-level compliant but left behind a stale define of
__ARCH_USE_5LEVEL_HACK in arch/arc/include/asm/hugepage.h.

Remove it.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>