Remove dynamic property definitions

Aims to fix deprecation warnings as highlighted by #91

engines/bittorrent/merge.php

@@ -1,5 +1,6 @@
 <?php
     class TorrentSearch extends EngineRequest {
+        protected $requests;
         public function __construct($opts, $mh) {
             parent::__construct($opts, $mh);
 

engines/invidious/video.php

@@ -1,5 +1,6 @@
 <?php
     class VideoSearch extends EngineRequest {
+        protected $instance_url;
         public function get_request_url() {
             $this->instance_url = $this->opts->invidious_instance_for_video_results;
             $query = urlencode($this->query);

engines/librex/fallback.php

@@ -1,6 +1,7 @@
 <?php
 
     class LibreXFallback extends EngineRequest {
+        protected $instance;
         public function __construct($instance, $opts, $mh) {
             $this->instance = $instance;
             parent::__construct($opts, $mh);

engines/special/wikipedia.php

@@ -1,5 +1,6 @@
 <?php
     class WikipediaRequest extends EngineRequest {
+        protected $wikipedia_domain;
         public function get_request_url() {
                 $this->wikipedia_domain = "wikipedia.org";
                 $query_encoded = urlencode($this->query);

engines/text/text.php

@@ -1,5 +1,6 @@
 <?php
     class TextSearch extends EngineRequest {
+        protected $engine, $engine_request, $special_request;
         public function __construct($opts, $mh) {
             $this->query = $opts->query;
             $this->page = $opts->page;

misc/search_engine.php

@@ -1,6 +1,8 @@
 <?php
     require "misc/cooldowns.php";
     abstract class EngineRequest {
+        protected $url, $query, $page, $opts, $mh, $ch;
+
         protected $DO_CACHING = true;
         function __construct($opts, $mh) {
             $this->query = $opts->query;