Remove is_qt4 checks

[aaronayres35]

Targeting stop-testing-pyqt4. This PR sits on top of #851 and removes is_qt4 checks from the code base.

[rahulporuri]

We can't remove code that handles qt4 from the codebase yet. Removing it from the testsuite is still acceptable but not from the package itself. We'll have to close/shelve this (and PRs like these until later).

[aaronayres35]

We can't remove code that handles qt4 from the codebase yet. Removing it from the testsuite is still acceptable but not from the package itself. We'll have to close/shelve this (and PRs like these until later).

I sort of figured this was too much too soon, but opened the PR anyway as it was fresh on my mind. We can shelve these until they are ready

[corranwebster]

This is fixed by #1043