This is more correct and may reduce the likelihood of perpetuating a bad
mixed-auth state.
In general, we should probably be modifying session and JWT cookies in
sync at all times, never individually. This specific code probably won't
make anything worse, but a clean reset might improve user experience in
the rare cases where someone somehow gets their browser into a weird
state.
- Switch from `response.set_cookie` with past expiry to just using the
`response.delete_cookie` method.
- Docstring improvements.
ref: ARCHBOM-2030 (internal)
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