We've decided to go in a different direction on indicating the staged
status of hunks, so go back for now to a world where we don't display
staged and unstaged hunks differently outside the (still gated) project
diff editor.

cc @iamnbutler 

This reverts commit 8c202b3b09083e0b5430fce3631734de6112bbc0.

Release Notes:

- N/A