[infra] Remove bookmaker bots

We've decided to move in a different direction for Skia documentation.

Bug: skia:
Change-Id: I4acfe06e412006cdd3d692d017e51ecf3e98f4c3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/198162
Commit-Queue: Eric Boren <borenet@google.com>
Reviewed-by: Ben Wagner <benjaminwagner@google.com>