rcutorture: Don't keep empty console.log.diags files

Currently, an error-free run produces an empty console.log.diags file.
This can be annoying when using "vi */console.log.diags" to see a full
summary of the errors.  This commit therefore removes any empty files
during the analysis process.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

tools/testing/selftests/rcutorture/bin/parse-console.sh

@@ -70,4 +70,6 @@ then
 		summary="$summary  Stalls: $n_stalls"
 	fi
 	print_warning Summary: $summary
+else
+	rm $1.diags
 fi