c34fc7f0b8
In the past, users had permission to edit their own legislation
proposals. However, that changed in commit ebfa3fb01, where we replaced
the `can` method with `cannot`.
An easier way to remove this permission is to simply remove the whole
statement, since by default users don't have permissions to do anything.
We're also adding a test checking users can't edit their own legislation
proposals, since it was missing.