Create `removeContentFromLibrary` method in ContentAPI

Create a specific API method for removing a content item from one's library. Also, there are likely specific permission bypassing that needs to be done in this scenario, and I'm not sure that these are tested in the unit tests.

E.g.,

1. UserA becomes a "viewer" of public ContentA
2. UserA removes ContentA from their library

Does it succeed even though UserA is not allowed to update ContentA's permissions?

Additional check likely needed for:

1. UserA becomes a "viewer" of public ContentB from public TenantB
2. ContentB becomes private
3. TenantB becomes private

UserA should be able to remove ContentB from their library, even though UserA crosses interaction boundaries with ContentB.