Move ID generation to xmpp folder

create_unique_id() was changed to use UUIDs instead of a counter in the
last commit. Since now it depends on connection_create_uuid() which is
in the xmpp subfolder the function should also be moved there.

Renamed it to connection_create_stanza_id() and moved it to
src/xmpp/connection.c.

Discussion happened in https://github.com/boothj5/profanity/pull/1010

src/common.c

@@ -56,7 +56,6 @@
 #include "log.h"
 #include "common.h"
 #include "tools/p_sha1.h"
-#include "xmpp/xmpp.h"
 
 struct curl_data_t
 {
@@ -331,27 +330,6 @@ release_is_new(char *found_version)
     }
 }
 
-char*
-create_unique_id(char *prefix)
-{
-    char *result = NULL;
-    GString *result_str = g_string_new("");
-    char *uuid = connection_create_uuid();
-
-    if (prefix) {
-        g_string_printf(result_str, "prof_%s_%s", prefix, uuid);
-    } else {
-        g_string_printf(result_str, "prof_%s", uuid);
-    }
-
-    connection_free_uuid(uuid);
-
-    result = result_str->str;
-    g_string_free(result_str, FALSE);
-
-    return result;
-}
-
 char*
 p_sha1_hash(char *str)
 {