plugins/stickykeys: Remove Id field from metadata

The Id field is obsolete in KF6. The filename of the so is used as the
plugin id.

src/plugins/stickykeys/metadata.json

@@ -1,6 +1,5 @@
 {
     "KPlugin": {
-        "EnabledByDefault": true,
-        "Id": "kwin5_plugin_stickykeys"
+        "EnabledByDefault": true
     }
 }