Revert "NonReparentingFocus - Reparent focus node in deactivate to match framework

[knopp]

This reverts commit 60bb442.

This causes some issues:

Tried to make a child into a parent of itself.
[***]: 'package:flutter/src/widgets/focus_manager.dart':
[***]: Failed assertion: line 1013 pos 12: 'child != this'
[***]: 
[***]: Either the assertion indicates an error in the framework itself, or we should provide substantially
[***]: more information in this error message to help you determine and fix the underlying cause.
[***]: In either case, please report this assertion by filing a bug on GitHub:
[***]:   https://github.com/flutter/flutter/issues/new?template=2_bug.yml
[***]: 
[***]: When the exception was thrown, this was the stack:
[***]: #2      FocusNode._reparent (package:flutter/src/widgets/focus_manager.dart:1013:12)
[***]: #3      FocusAttachment.reparent (package:flutter/src/widgets/focus_manager.dart:255:14)
[***]: #4      _NonReparentingFocusState.deactivate (package:super_editor/src/infrastructure/focus.dart:58:30)
[***]: #5      StatefulElement.deactivate (package:flutter/src/widgets/framework.dart:5683:11)

I think the reason for this is that FocusState from framework reparents itself to parent during build() for reasons not entirely clean to me. It's a fragile system and rolling custom focus widget seem to break some assumptions that rest of the framework does (i.e. related focus scope caching that was added recently).

I think we should figure out whether NonReparentingNode is necessary at all in the presence of OverlayPortal and if not remove it completely.

[knopp]

cc @angelosilvestre @matthew-carroll

[matthew-carroll]

@angelosilvestre can you cherry pick this reversion?