remove rails 6.1 deprecation notice from CET specs
remove rails 6.1 deprecation notice from CET specs

why:
* the context_external_tool's visible scope uses a scope inside
the method that is supposed to not be enclosed by `visible`,
but will be starting with Rails 6.1
* this was causing DEPRECATION WARNINGs when running specs,
and these specs probably fail with Rails 6.1

refs INTEROP-7067
flag=none

test plan:
* tbd but it involves exercising LTI launch definitions
(think adding a module item or assignment launch)
with a tool that has a visibility override for that placement
* and when a user doesn't have that visibility level, it shouldn't
show up
* and this process shouldn't break
* specs also take care of a lot of this

Change-Id: I99f9fa424ad7bbe8957e35af178e10fcf2487023
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/285654
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
Product-Review: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
Reviewed-by: Jacob Burroughs <8ecea6e385af5cf9f53123f5ca17fb5fd6a6d4b2@instructure.com>

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