deprecate draw text on path in docs

Remove documentation, see also references, and examples
that rely on SkCanvas::drawTextOnPath(HV).

Move example that uses SkDrawTextOnPath into illustrations.
TBR=reed@google.com

Docs-Preview: https://skia.org/?cl=150020
Bug: skia:6898
Change-Id: I1d92f258b75a8a10a6aa89ebf9380871ba7ecac5
Reviewed-on: https://skia-review.googlesource.com/150020
Commit-Queue: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@skia.org>
10 files changed