ANDROID: Drop mixed-build-prefix from Makefile.modinst.

This partially reverts the conflict resolution done by commit
51786e2d ("Merge 61401a87 ("Merge
tag 'kbuild-v6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild"

)
into android-mainline").

Now that KBUILD_MIXED_TREE is identical to objtree, there is no point
of prepending mixed-build-prefix here.

Bug: 402231876
Change-Id: Iac8b1fd4fc6a55d71f97b5ae71afb52feceb168d
Signed-off-by: HONG Yifan <elsk@google.com>

scripts/Makefile.modinst

@@ -35,7 +35,7 @@ install-y += $(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo)
 
 install-$(CONFIG_BUILTIN_MODULE_RANGES) += $(MODLIB)/modules.builtin.ranges
 
-$(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo modules.builtin.ranges): $(MODLIB)/%: $(mixed-build-prefix)% FORCE
+$(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo modules.builtin.ranges): $(MODLIB)/%: % FORCE
 	$(call cmd,install)
 
 endif