delete textonpath code -- not used anywhere

Bug: skia:
Change-Id: Ib645f7c140f87123429170a0bf6f7ed86ce53b3f
Reviewed-on: https://skia-review.googlesource.com/158224
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
13 files changed