kbuild: remove warning about "make depend"

Enough time has passed since "make depend" was deprecated.
Nobody would be in trouble without this hint.
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Makefile

@@ -1025,12 +1025,6 @@ headerdep:
 	$(Q)find $(srctree)/include/ -name '*.h' | xargs --max-args 1 \
 	$(srctree)/scripts/headerdep.pl -I$(srctree)/include
 
-# ---------------------------------------------------------------------------
-
-PHONY += depend dep
-depend dep:
-	@echo '*** Warning: make $@ is unnecessary now.'
-
 # ---------------------------------------------------------------------------
 # Firmware install
 INSTALL_FW_PATH=$(INSTALL_MOD_PATH)/lib/firmware