mm: drop unused pmdp_huge_get_and_clear_notify()

Dave noticed that after fixing MADV_DONTNEED vs numa balancing race the
last pmdp_huge_get_and_clear_notify() user is gone.

Let's drop the helper.

Link: http://lkml.kernel.org/r/20170306112047.24809-1-kirill.shutemov@linux.intel.com


Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>