Fix issues in changed files

- Initializes $return in Process::insert
- Update the type hint of dba::fetch
- Remove unused $a parameter in worker_init()
- Fix uses

mod/worker.php

@@ -4,11 +4,10 @@
  * @brief Module for running the worker as frontend process
  */
 
-use Friendica\Core\Worker;
 use Friendica\Core\Config;
-use Friendica\Core\PConfig;
+use Friendica\Core\Worker;
 
-function worker_init($a){
+function worker_init(){
 
 	if (!Config::get("system", "frontend_worker")) {
 		return;