selftests: mm: remove wrong kernel header inclusion

It is wrong to include unprocessed user header files directly.  They are
processed to "<source_tree>/usr/include" by running "make headers" and
they are included in selftests by kselftest makefiles automatically with
help of KHDR_INCLUDES variable.  These headers should always bulilt first
before building kselftests.

Link: https://lkml.kernel.org/r/20230612095347.996335-1-usama.anjum@collabora.com


Fixes: 07115fcc ("selftests/mm: add new selftests for KSM")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>