s390-tools: Move function util_strstrip

This patch
 - moves function util_strstrip to libutil/util_libc.c and deletes the
   extra files util_strstip.[ch]
 - adds doxygen comments for util_strstrip()
 - provides an example on how to use util_strstrip().

Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

libutil/util_str.c

@@ -1,39 +0,0 @@
-/*
- * util - Utility function library
- *
- * Strip leading and trailing blanks.
- *
- * Copyright IBM Corp. 2018
- *
- * s390-tools is free software; you can redistribute it and/or modify
- * it under the terms of the MIT license. See LICENSE for details.
- */
-
-#include <string.h>
-#include <ctype.h>
-
-#include "lib/util_str.h"
-
-/*
- * strip leading and trailing blanks
- */
-char *util_strstrip(char *s)
-{
-	size_t size;
-	char *end;
-
-	size = strlen(s);
-
-	if (!size)
-		return s;
-
-	end = s + size - 1;
-	while (end >= s && isspace(*end))
-		end--;
-	*(end + 1) = '\0';
-
-	while (*s && isspace(*s))
-		s++;
-
-	return s;
-}