BaseWebAPITestCase was a very old class with a lot of legacy functions

that were no longer used. With some changes coming up, it was a good

time to remove these and clean up the code.
All the utility functions for creating and deleting certain types of

objects have been removed. Only one was in use, and only in one place,

so the functionality has intstead been moved into the unit test that

needs it.
We now have typing throughout the class, cleanup of state post-test,

proper documentation, and performance improvements for user login.
The performance improvements remove an unnecessary redundant User

query when logging in an administrator on Local Sites. We were querying

for the same user twice. Along with that, we now use a different login

method that lets us pass in an explicit User, avoiding auth backend

lookups and even more User queries. These save between 10-15 seconds

from the API unit tests locally (there's some variance due to repository

access).

All unit tests pass.