Revert "hugetlbfs: flush TLBs correctly after huge_pmd_unshare"

This reverts commit 7bf1f5cb to reapply it with changes in accordance with an upcoming commit that moves the TLB flushing logic into mmu_gather.c.

Change-Id: I706c51a56b083669f70822d6ad148f2d6f91d8bf
Signed-off-by: Cyber Knight <cyberknight755@gmail.com>