console.c: Use prefs_free_string()

f9961677aa  replaces prefs_free_string()
with g_free(). Both is correct but lets still use this.

src/ui/console.c

@@ -2068,7 +2068,7 @@ cons_executable_setting(void)
 {
     char *avatar = prefs_get_string(PREF_AVATAR_CMD);
     cons_show("'/avatar' command (/executable avatar)                                   : %s", avatar);
-    g_free(avatar);
+    prefs_free_string(avatar);
 
     char **urlopen = prefs_get_string_list_with_option(PREF_URL_OPEN_CMD, "");
     cons_show("Default '/url open' command (/executable urlopen)                        : %s", urlopen[1]);