LTI, investigate: JWKS, LTIException, and scope updates

[lsloan]

Originally posted by @lsloan in #1421 (comment)

Following a discussion in Slack (see PDF here or in Google Drive), the PR for #1387 was reverted because Canvas requires JWKS support even when it's not going to be used.

The intent of #1387 was to remove definition of LTIException, referrals to it, apparently unused JWKS functions, and cleaning up (removing) the LTI scope. It turns out that Canvas requires the JWKS support functions, even though the PR had been approved.

In this issue, investigate and determine whether these things can be done.

• – Remove JWKS support. Does Canvas really require this, even when it's not used by the application? If the support cannot be removed, can it be reduced to something simple, like returning a dummy value?
• – Remove LTIException definition. Is this exception definition really necessary? Can it be removed or left uncaught?
• – Remove the scopes. As was done in PR remove LTIException & referencing functions (iss. #1387) #1421 for the original issue remove the scopes, because they are unneeded.