kbuild: remove duplicated arch/*/include/generated/uapi include path

Commit 90ac086 ("Makefile: include arch/*/include/generated/uapi
before .../generated") introduced this for bisect'ability.  The commit
chose to promote arch/*/include/generated/uapi in the search path
rather than cleaning stale headers.

After all, we found that approach was not enough, and ended up with
cleaning stale headers by commit cda2c65 ("kbuild: Remove stale
asm-generic wrappers").

So, the extra search path is no longer needed because Kbuild invokes
scripts/Makefile.asm-generic and remove stale headers before it starts
descending.

This commit is also reverting commit dc33db7 ("Kbuild: avoid
duplicate include path") because we have no more duplicated path.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -381,12 +381,10 @@ USERINCLUDE    := \
 # Needed to be compatible with the O= option
 LINUXINCLUDE    := \
 		-I$(srctree)/arch/$(hdr-arch)/include \
-		-I$(objtree)/arch/$(hdr-arch)/include/generated/uapi \
 		-I$(objtree)/arch/$(hdr-arch)/include/generated \
 		$(if $(KBUILD_SRC), -I$(srctree)/include) \
-		-I$(objtree)/include
-
-LINUXINCLUDE	+= $(filter-out $(LINUXINCLUDE),$(USERINCLUDE))
+		-I$(objtree)/include \
+		$(USERINCLUDE)
 
 KBUILD_CPPFLAGS := -D__KERNEL__