Remove mdbviz

The MultiDrawBuffer no longer exists.

Change-Id: I31c2df9a5363daab018e33156104e3dd7904230e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/532012
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
11 files changed