tag_pool: use GStaticMutex

Eliminates explicit global initialisation.

test/run_decoder.c

@@ -21,7 +21,6 @@
 #include "io_thread.h"
 #include "decoder_list.h"
 #include "decoder_api.h"
-#include "tag_pool.h"
 #include "input_init.h"
 #include "input_stream.h"
 #include "audio_format.h"
@@ -191,8 +190,6 @@ int main(int argc, char **argv)
 		return EXIT_FAILURE;
 	}
 
-	tag_pool_init();
-
 	if (!input_stream_global_init(&error)) {
 		g_warning("%s", error->message);
 		g_error_free(error);
@@ -248,7 +245,5 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	tag_pool_deinit();
-
 	return 0;
 }