perf tools: Remove unused 'prefix' from builtin functions

We got it from the git sources but never used it for anything, with the
place where this would be somehow used remaining:

  static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
  {
	prefix = NULL;
	if (p->option & RUN_SETUP)
		prefix = NULL; /* setup_perf_directory(); */

Ditch it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-uw5swz05vol0qpr32c5lpvus@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-data.c b/tools/perf/builtin-data.c
index 7ad6e17..0adb5f8 100644
--- a/tools/perf/builtin-data.c
+++ b/tools/perf/builtin-data.c
@@ -6,7 +6,7 @@
 #include "data-convert.h"
 #include "data-convert-bt.h"
 
-typedef int (*data_cmd_fn_t)(int argc, const char **argv, const char *prefix);
+typedef int (*data_cmd_fn_t)(int argc, const char **argv);
 
 struct data_cmd {
 	const char	*name;
@@ -50,8 +50,7 @@ static const char * const data_convert_usage[] = {
 	NULL
 };
 
-static int cmd_data_convert(int argc, const char **argv,
-			    const char *prefix __maybe_unused)
+static int cmd_data_convert(int argc, const char **argv)
 {
 	const char *to_ctf     = NULL;
 	struct perf_data_convert_opts opts = {
@@ -98,7 +97,7 @@ static struct data_cmd data_cmds[] = {
 	{ .name = NULL, },
 };
 
-int cmd_data(int argc, const char **argv, const char *prefix)
+int cmd_data(int argc, const char **argv)
 {
 	struct data_cmd *cmd;
 	const char *cmdstr;
@@ -118,7 +117,7 @@ int cmd_data(int argc, const char **argv, const char *prefix)
 		if (strcmp(cmd->name, cmdstr))
 			continue;
 
-		return cmd->fn(argc, argv, prefix);
+		return cmd->fn(argc, argv);
 	}
 
 	pr_err("Unknown command: %s\n", cmdstr);