Delete kani::expect_fail and associated hook

[zhassan-aws]

Description of changes:

Get rid of kani::expect_fail, and replace its usage in the regressions by kani::cover.

Resolved issues:

Resolves #1197
Resolves #1538

Related RFC:

Optional #ISSUE-NUMBER.

Call-outs:

There were many _fail tests that used kani::expect_fail that had a corresponding non-failing test that used assert. For example, a test name foo.rs would have:

let x = ...
assert!(x == 2);

and there would be a corresponding test named foo_fail.rs that has:

let x = ...
kani::expect_fail(x != 2);

These tests were essentially useless (since the main test verifies that the assertion passes), so I deleted all of them.

I only kept tests that were meaningful, and replaced kani::expect_fail with kani::cover.

Testing:

• How is this change tested? Updated regressions

• Is this a refactor change? No

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[celinval]

That's awesome! Thanks for doing this. Question, did you mean to delete or replace the DynTrait tests?