Use `#kani_comment` instead of `#comment` for deinit

[giltho]

Description of changes:

Instead of inserting a comment field on the Irep for deinit and potential future annotations, inserts a #kani_comment. It seems that having a field that doesn't that with a # might be dangerous otherwise.

Resolved issues:

Resolves #1575

Call-outs:

Kani still outputs some comment fields, as it used to before #1469, but these comment fields are inside a #c_location field, so they will be ignored by transitivity.

Testing:

This is just a slight change, it should not change anything in kani.

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

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