build: silence false errors during make clean

Author: theuni

src/Makefile.am

@@ -276,7 +276,7 @@ EXTRA_DIST = leveldb secp256k1
 
 clean-local:
 	-$(MAKE) -C leveldb clean
-	-$(MAKE) -C secp256k1 clean
+	-$(MAKE) -C secp256k1 clean 2>/dev/null
 	rm -f leveldb/*/*.gcno leveldb/helpers/memenv/*.gcno
 	-rm -f config.h