Clean up debug output

Remove the unnecessary util.c/util.h files and use purple_debug_info()
throughout instead. This is more direct. Also replace all usages of
printf() with the same helper.

This makes the Delta plugin usable in command-line applications like
Finch. Previously, the printf() output was messing up the screen!

libdelta.c

@@ -78,8 +78,6 @@ delta_init_plugin(PurplePlugin *plugin)
 	PurplePluginProtocolInfo *extra = (PurplePluginProtocolInfo *)plugin->info->extra_info;
 	GList *opts = NULL;
 
-	debug("Starting up\n");
-
 	opts = g_list_prepend(opts, str_opt("Display Name", PLUGIN_ACCOUNT_OPT_DISPLAY_NAME, NULL));
 
 	opts = g_list_prepend(opts, str_opt("IMAP Server Host", PLUGIN_ACCOUNT_OPT_IMAP_SERVER_HOST, NULL));
@@ -106,8 +104,6 @@ delta_init_plugin(PurplePlugin *plugin)
 static void
 delta_destroy_plugin(PurplePlugin *plugin) {
 	UNUSED(plugin);
-
-	debug("Shutting down\n");
 }
 
 static gboolean