Revert "Enable Qt message loop on Linux"

[tytan652]

Description

Closes obsproject/obs-studio#11485

This reverts commit 98d94a4.

Motivation and Context

Performance were met by multiple users.

So back to use_gtk=false builds.

How Has This Been Tested?

Used use_gtk=false for testing (even tested with #453) everything seem to work properly.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

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.