fix(container_window): remove createWindowContainer

Having `createWindowContainer` in `QVTKRenderWindowInteractor` is
causing segfaults. Instead, teach users to add

```python
window_ = QtGui.QWindow.fromWinId(self.plotter.winId())
self.container = self.createWindowContainer(window_, self)
```

to their `MainWindow` class.

pyvistaqt/plotting.py

@@ -55,7 +55,7 @@
 from pyvista.plotting.plotting import BasePlotter
 from pyvista.plotting.render_window_interactor import RenderWindowInteractor
 from pyvista.utilities import conditional_decorator, threaded
-from qtpy import QtCore
+from qtpy import QtCore, QtWidgets
 from qtpy.QtCore import QSize, QTimer, Signal
 from qtpy.QtWidgets import (
     QAction,
@@ -270,9 +270,6 @@ def __init__(
         self._first_time = False  # Crucial!
         LOG.debug("QtInteractor init stop")
 
-        window_ = QtGui.QWindow.fromWinId(self.winId())
-        self.createWindowContainer(window_, self)
-
     def _setup_interactor(self, off_screen: bool) -> None:
         if off_screen:
             self.iren: Any = None