MODSIGN: Make mrproper should remove generated files.

It doesn't, because the clean targets don't include kernel/Makefile, and
because two files were missing from the list.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Makefile

@@ -995,7 +995,10 @@ MRPROPER_DIRS  += include/config usr/include include/generated          \
                   arch/*/include/generated
 MRPROPER_FILES += .config .config.old .version .old_version             \
                   include/linux/version.h                               \
-		  Module.symvers tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS
+		  Module.symvers tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS \
+		  signing_key.priv signing_key.x509 x509.genkey		\
+		  extra_certificates signing_key.x509.keyid		\
+		  signing_key.x509.signer
 
 # clean - Delete most, but leave enough to build external modules
 #

kernel/Makefile

@@ -208,4 +208,3 @@ x509.genkey:
 	@echo >>x509.genkey "subjectKeyIdentifier=hash"
 	@echo >>x509.genkey "authorityKeyIdentifier=keyid"
 endif
-CLEAN_FILES += signing_key.priv signing_key.x509 x509.genkey extra_certificates