Lock down the trash collection more (#45866)

* Lock down the trash collection more

Oops. I was very thorough in checking that you couldn't modify the
trash collection in the sense of moving things to or from it. I missed
the most obvious thing: actually modifying the trash collection itself.
So if someone wanted, they could change the name of the Trash to
"Definitely Not the Trash".

* Remove the Trash Collection from serialization

Serialization tests were failing due to the previous change, but this
got me thinking, and I realized that serializing the Trash collection is
completely unnecessary. We want to create it programatically on
startup (which we are) and then nothing should change it afterwards.