Cleanup unnecessary code in canvas_skia
* Removed AdjustStringDirection()
* Removed FORCE_XXXX_DIRECTIONALITY and replace with TEXT_ALIGN_TO_HEAD. This is necessary not to use Canvas::DefaultCanvasTextAlignment for labels.
* Also removed the safe guard in SizeStringFloat because RenderTextWin has been removed.
BUG=None
TEST=No functional change. Removed LabelTest, DirectionalityFromText that no longer makes sense.
R=msw@chromium.org
Review URL: https://codereview.chromium.org/
953093003
Cr-Commit-Position: refs/heads/master@{#319166}