perf tools: Remove needless 'extern' from function prototypes

Cc: Adrian Hunter <adrian.hunter@intel.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-w246stf7ponfamclsai6b9zo@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
index 2080142..46d4dd0 100644
--- a/tools/perf/util/util.h
+++ b/tools/perf/util/util.h
@@ -133,17 +133,17 @@
 #define PERF_GTK_DSO  "libperf-gtk.so"
 
 /* General helper functions */
-extern void usage(const char *err) NORETURN;
-extern void die(const char *err, ...) NORETURN __attribute__((format (printf, 1, 2)));
-extern int error(const char *err, ...) __attribute__((format (printf, 1, 2)));
-extern void warning(const char *err, ...) __attribute__((format (printf, 1, 2)));
+void usage(const char *err) NORETURN;
+void die(const char *err, ...) NORETURN __attribute__((format (printf, 1, 2)));
+int error(const char *err, ...) __attribute__((format (printf, 1, 2)));
+void warning(const char *err, ...) __attribute__((format (printf, 1, 2)));
 
 #include "../../../include/linux/stringify.h"
 
-extern void set_warning_routine(void (*routine)(const char *err, va_list params));
+void set_warning_routine(void (*routine)(const char *err, va_list params));
 
-extern int prefixcmp(const char *str, const char *prefix);
-extern void set_buildid_dir(const char *dir);
+int prefixcmp(const char *str, const char *prefix);
+void set_buildid_dir(const char *dir);
 
 #ifdef __GLIBC_PREREQ
 #if __GLIBC_PREREQ(2, 1)
@@ -164,8 +164,8 @@
 /*
  * Wrappers:
  */
-extern char *xstrdup(const char *str);
-extern void *xrealloc(void *ptr, size_t size) __attribute__((weak));
+char *xstrdup(const char *str);
+void *xrealloc(void *ptr, size_t size) __attribute__((weak));
 
 
 static inline void *zalloc(size_t size)