build: remove package preconfig feature

This feature has been unused for years, and its scope is too limited to be
actually useful.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

package/Makefile

@@ -72,7 +72,6 @@ $(curdir)/install: $(TMP_DIR)/.build $(curdir)/merge $(if $(CONFIG_TARGET_PER_DE
 			$(call opkg,$(TARGET_DIR)) flag $$flag `cat $$file`; \
 		done; \
 	done || true
-	@-$(MAKE) package/preconfig
 
 	$(CP) $(TARGET_DIR) $(TARGET_DIR_ORIG)
 
@@ -96,8 +95,6 @@ ifdef CONFIG_SIGNED_PACKAGES
 	); done
 endif
 
-$(curdir)/preconfig:
-
 $(curdir)/flags-install:= -j1
 
 $(eval $(call stampfile,$(curdir),package,prereq,.config))