perf tools: Ditch rtrim(), use skip_spaces() to get closer to the kernel

No change in behaviour, just using the same kernel idiom for such
operation.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: André Goddard Rosa <andre.goddard@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-a85lkptkt0ru40irpga8yf54@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/string.c

@@ -318,20 +318,6 @@ char *strxfrchar(char *s, char from, char to)
 	return s;
 }
 
-/**
- * ltrim - Removes leading whitespace from @s.
- * @s: The string to be stripped.
- *
- * Return pointer to the first non-whitespace character in @s.
- */
-char *ltrim(char *s)
-{
-	while (isspace(*s))
-		s++;
-
-	return s;
-}
-
 /**
  * rtrim - Removes trailing whitespace from @s.
  * @s: The string to be stripped.