forms: Remove Qt<6.10 code

[RytoEX]

Description

Qt 6.10 is the minimum supported Qt version now.

Motivation and Context

Want to remove old Qt code paths.

How Has This Been Tested?

Tested OS(s):
Windows 11 - compiled and ran and loaded the WebSocket Server Settings dialog.

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• I have read the Contributing Guidelines.
• All commit messages are properly formatted and commits squashed where appropriate.
• My code is not on master or a release/* branch.
• The code has been tested.
• I have included updates to all appropriate documentation.