Remove Library.all_collections property.

[tdilauro]

Description

Removes Library.all_collections (and its functionality), replaces its usage with Library.collections, and removes a test assertion specific to this method.

Motivation and Context

While working on PP-1875, I ran into this attribute, which provides a generator that yields both the collections associated with a library and the parents of those collections, where present.

It came in on this commit on this PR.

Here's some context from the PR description:

When I tried setting up an Overdrive Advantage collection, I expected that I would be able to add the Overdrive Advantage collection to a library and have that library’s feeds also contain the books from the parent consortium collection. Without this change, I’d have to separately add the consortium collection to the library.

The downside is that now there’s no way to get a feed that has the Overdrive Advantage books without the consortium’s books.

So, based on how we currently configure our collections that have parents -- specifically, we configure the library association for both OD main accounts and Advantage accounts, as appropriate -- I don't think we need the functionality it provides.

How Has This Been Tested?

• Tests pass locally.
• CI tests for associated branch pass.

Checklist

• N/A - I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.05%. Comparing base (8d10cab) to head (48d5c9c).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2191      +/-   ##
==========================================
- Coverage   91.05%   91.05%   -0.01%     
==========================================
  Files         363      363              
  Lines       41218    41213       -5     
  Branches     8847     8845       -2     
==========================================
- Hits        37530    37525       -5     
  Misses       2417     2417              
  Partials     1271     1271              

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[jonathangreen]

Looks good!