Move internal plugins into plugin-folder

Stepping stone to later use spartacus for all of them. Will break installed plugins

include/plugin_api.inc.php

@@ -489,9 +489,7 @@ class serendipity_plugin_api
 
         // First try the local path, and then (if existing) a shared library repository ...
         // Internal plugins ignored.
-        if (!empty($instance_id) && $instance_id[0] == '@') {
-            $file = S9Y_INCLUDE_PATH . 'include/plugin_internal.inc.php';
-        } elseif (file_exists($serendipity['serendipityPath'] . $pluginFile)) {
+        if (file_exists($serendipity['serendipityPath'] . $pluginFile)) {
             $file = $serendipity['serendipityPath'] . $pluginFile;
         } elseif (file_exists(S9Y_INCLUDE_PATH . $pluginFile)) {
             $file = S9Y_INCLUDE_PATH . $pluginFile;
@@ -1697,8 +1695,4 @@ class serendipity_event extends serendipity_plugin
 
 }
 
-if (!defined('S9Y_FRAMEWORK_PLUGIN_INTERNAL')) {
-    include S9Y_INCLUDE_PATH . 'include/plugin_internal.inc.php';
-}
-
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