system/mtd: drop Build/Prepare rule in favor of default one

Signed-off-by: Alexandru Ardelean <[email protected]>

package/system/mtd/Makefile

@@ -31,11 +31,6 @@ define Package/mtd/description
  older OpenWrt releases.
 endef
 
-define Build/Prepare
-	mkdir -p $(PKG_BUILD_DIR)
-	$(CP) ./src/* $(PKG_BUILD_DIR)/
-endef
-
 target=$(firstword $(subst -, ,$(BOARD)))
 
 MAKE_FLAGS += TARGET="$(target)"