perf ui gtk: Move gtk .so name to the only place where it is used

No need to pollute util.h with this.

Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-kec0chbdtgrd71o3oi2kz2zt@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.h

@@ -22,8 +22,6 @@
 #endif
 #endif
 
-#define PERF_GTK_DSO  "libperf-gtk.so"
-
 /* General helper functions */
 void usage(const char *err) NORETURN;
 void die(const char *err, ...) NORETURN __attribute__((format (printf, 1, 2)));