Revert "Add PopupVoid (#734)" (#739)

This reverts commit 90d6944290.

ext/fg/js/popup-void.js

@@ -1,126 +0,0 @@
-/*
- * Copyright (C) 2020  Yomichan Authors
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
-
-/**
- * A void popup with no functionality, usable as a placeholder.
- */
-class PopupVoid {
-    constructor(id, depth, frameId, ownerFrameId) {
-        this._id = id;
-        this._depth = depth;
-        this._frameId = frameId;
-        this._ownerFrameId = ownerFrameId;
-        this._parent = null;
-        this._child = null;
-    }
-
-    // Public properties
-
-    get id() {
-        return this._id;
-    }
-
-    get parent() {
-        return this._parent;
-    }
-
-    set parent(value) {
-        this._parent = value;
-    }
-
-    get child() {
-        return this._child;
-    }
-
-    set child(value) {
-        this._child = value;
-    }
-
-    get depth() {
-        return this._depth;
-    }
-
-    get frameContentWindow() {
-        return null;
-    }
-
-    get container() {
-        return null;
-    }
-
-    // Public functions
-
-    prepare() {
-        // NOP
-    }
-
-    async setOptionsContext(_optionsContext, _source) {
-        // NOP
-    }
-
-    hide(_changeFocus) {
-        // NOP
-    }
-
-    async isVisible() {
-        return false;
-    }
-
-    setVisibleOverride(_visible) {
-        // NOP
-    }
-
-    async containsPoint(_x, _y) {
-        return false;
-    }
-
-    async showContent(_details, _displayDetails) {
-        // NOP
-    }
-
-    setCustomCss(_css) {
-        // NOP
-    }
-
-    clearAutoPlayTimer() {
-        // NOP
-    }
-
-    setContentScale(_scale) {
-        // NOP
-    }
-
-    isVisibleSync() {
-        return false;
-    }
-
-    updateTheme() {
-        // NOP
-    }
-
-    async setCustomOuterCss(_css, _useWebExtensionApi) {
-        return null;
-    }
-
-    setChildrenSupported(_value) {
-        // NOP
-    }
-
-    getFrameRect() {
-        return new DOMRect(0, 0, 0, 0);
-    }
-}