Fix make clobber in 2020/yang

The file wrongcoded is now removed.

This should fix the make www step of verify_entry_files which allows all
of it to complete (should because I did not test make www but the direct
command that is run on 2020/yang now exits 0).

2020/yang/Makefile

@@ -209,7 +209,7 @@ clean:
 
 clobber: clean
 	${RM} -f ${TARGET} ${ALT_TARGET}
-	${RM} -rf *.dSYM decoded code.c encoded.c
+	${RM} -rf *.dSYM decoded code.c encoded.c wrongcoded
 	@-if [ -e sandwich ]; then \
 	    ${RM} -f sandwich; \
 	    echo 'ate sandwich'; \