kbuild: remove 'prepare1' target

Now that there is no rule for 'prepare1', it can go away.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -1089,7 +1089,7 @@ scripts: scripts_basic scripts_dtc
 # archprepare is used in arch Makefiles and when processed asm symlink,
 # version.h and scripts_basic is processed / created.
 
-PHONY += prepare archprepare prepare1 prepare3
+PHONY += prepare archprepare prepare3
 
 # prepare3 is used to check if we are building in a separate output directory,
 # and if so do:
@@ -1106,10 +1106,8 @@ ifdef building_out_of_srctree
 	fi;
 endif
 
-prepare1: prepare3 outputmakefile asm-generic $(version_h) $(autoksyms_h) \
-						include/generated/utsrelease.h
-
-archprepare: archheaders archscripts prepare1 scripts
+archprepare: archheaders archscripts scripts prepare3 outputmakefile \
+	asm-generic $(version_h) $(autoksyms_h) include/generated/utsrelease.h
 
 prepare0: archprepare
 	$(Q)$(MAKE) $(build)=scripts/mod