Clean up revertLastWord()

The "deleteChar" argument of this method is acutally always true in the current code path.
Also, in this method, textToTheLeft virtually never has a punctuation letter as its initial
character.  This change is one of preparatory changes for bug:4983945.

Change-Id: I531a32570a35634c21c1d74b2b461e40a1b7f660