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>

tools/testing/selftests/mm/Makefile

@@ -29,7 +29,7 @@ MACHINE ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/p
 # LDLIBS.
 MAKEFLAGS += --no-builtin-rules
 
-CFLAGS = -Wall -I $(top_srcdir) -I $(top_srcdir)/tools/include/uapi $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
+CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
 LDLIBS = -lrt -lpthread
 
 TEST_GEN_PROGS = cow