Revert "userfaultfd: selftest: vm: allow to build in vm/ directory"

This reverts commit b5213e1e which was
commit 46aa6a30 upstream.

This is being reverted because the affected commit this was trying to
fix, a8ba798b ("selftests: enable O and KBUILD_OUTPUT"), was never
backported to the 4.4-stable tree.
Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/testing/selftests/vm/Makefile

 # Makefile for vm selftests
 
-ifndef OUTPUT
-  OUTPUT := $(shell pwd)
-endif
-
 CFLAGS = -Wall -I ../../../../usr/include $(EXTRA_CFLAGS)
 BINARIES = compaction_test
 BINARIES += hugepage-mmap