Revert "UI: Restore XDG config path update for FreeBSD"

[emaste]

Description

To support upgrades from older versions move_to_xdg was reintroduced for FreeBSD. This has now been available since release 31.0, so users have likely upgraded across this version and it is no longer needed.

Motivation and Context

Clean up no longer needed code.

This reverts commit 39b91d8.
It is essentially c053216 reapplied.

How Has This Been Tested?

Verified that obs still uses expected XDG path (~/.config/obs-studio/) with this change applied.

Types of changes

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

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[emaste]

(updated commit message to specify frontend; I did this change originally before the move, and have been rebasing since)