Remove title accessors from WebDataSource.

These are no longer necessary as of
http://src.chromium.org/viewvc/chrome?view=revision&revision=217846

BUG=none

Review URL: https://chromiumcodereview.appspot.com/23172004

git-svn-id: svn://svn.chromium.org/blink/trunk@156327 bbb929c8-8fbe-4397-9dbb-9b2b20218538