Cleanup tons of obsolete commented out code

Mostly in EditorNode, dropping some obsolete editor plugins and also a
cleanup of ProjectSettings/EditorSettings.

editor/plugins/material_editor_plugin.cpp

@@ -27,12 +27,14 @@
 /* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
+
+// FIXME: Disabled as (according to reduz) users were complaining that it gets in the way
+// Waiting for PropertyEditor rewrite (planned for 3.1) to be refactored.
+#if 0
 #include "material_editor_plugin.h"
 
 #include "scene/main/viewport.h"
 
-#if 0
-
 void MaterialEditor::_gui_input(InputEvent p_event) {