BUG_FIX: Revert part of WindowLevel fix.

Commit 7f08be80c60f3ab761155fd03a91077aa6b22ef0 caused Window and Level to not work on several of my applications. This commit reverses the fix.
Merge branch 'Branch_v5.10.1' of https://github.com/drescherjm/VTK into Branch_v5.10.1