MDL-56320 webservice: Allow uninstall of unused plugins

admin/tool/mobile/version.php

@@ -26,3 +26,6 @@ defined('MOODLE_INTERNAL') || die();
 $plugin->version   = 2016052305; // The current plugin version (Date: YYYYMMDDXX).
 $plugin->requires  = 2016051900; // Requires this Moodle version.
 $plugin->component = 'tool_mobile'; // Full name of the plugin (used for diagnostics).
+$plugin->dependencies = array(
+    'webservice_rest' => 2016052300
+);

lib/classes/plugininfo/webservice.php

@@ -79,6 +79,10 @@ class webservice extends base {
     }
 
     public function is_uninstall_allowed() {
-        return false;
+        // The xmlrpc plugin contains webservice_xmlrpc_client (used by core).
+        if ($this->name == 'xmlrpc') {
+            return false;
+        }
+        return true;
     }
 }