Makefile: drop gen-missing-cpe leftovers

In 6fa3a239 the gen-missing-cpe support script was removed together with
"make missing-cpe".
Remove the leftover path variable and drop it from "make clean".

Signed-off-by: Daniel Lang <dalang@gmx.at>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Makefile

@@ -227,8 +227,6 @@ LEGAL_MANIFEST_CSV_HOST = $(LEGAL_INFO_DIR)/host-manifest.csv
 LEGAL_WARNINGS = $(LEGAL_INFO_DIR)/.warnings
 LEGAL_REPORT = $(LEGAL_INFO_DIR)/README
 
-CPE_UPDATES_DIR = $(BASE_DIR)/cpe-updates
-
 BR2_CONFIG = $(CONFIG_DIR)/.config
 
 # Pull in the user's configuration file
@@ -1104,8 +1102,7 @@ show-vars:
 clean:
 	rm -rf $(BASE_TARGET_DIR) $(BINARIES_DIR) $(HOST_DIR) $(HOST_DIR_SYMLINK) \
 		$(BUILD_DIR) $(BASE_DIR)/staging \
-		$(LEGAL_INFO_DIR) $(GRAPHS_DIR) $(PER_PACKAGE_DIR) $(CPE_UPDATES_DIR) \
-		$(O)/pkg-stats.*
+		$(LEGAL_INFO_DIR) $(GRAPHS_DIR) $(PER_PACKAGE_DIR) $(O)/pkg-stats.*
 
 .PHONY: distclean
 distclean: clean