remove unused gem testingbot
remove unused gem testingbot

it's not compatible with ruby 3 and it hasn't been used since
we stopped running selenium specs on internet explorer

Change-Id: Iad79eeb57b4ce7a1f972e223278accef79966a99
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/285262
Reviewed-by: Jacob Burroughs <8ecea6e385af5cf9f53123f5ca17fb5fd6a6d4b2@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms