Remove the webcore.py gdb pretty printer.

It has been only a placeholder for backwards compatibility for almost 3
years, so it should be pretty safe to remove it now.

R=dpranke@chromium.org,ojan@chromium.org,jochen@chromium.org

Review URL: https://chromiumcodereview.appspot.com/17619011

git-svn-id: svn://svn.chromium.org/blink/trunk@153000 bbb929c8-8fbe-4397-9dbb-9b2b20218538