Cleanup | Remove unused members

[edwardneal]

Description

This continues mop-up work which started to come into focus during the merge. It also lays the groundwork for two pieces of future work.

There were a handful of members which were never used. This PR removes them.

We also lay the groundwork for two future pieces of work:

1. Removing unused members from SqlUtil.cs and AdapterUtil.cs also removes references to a few resource strings. When this and Cleanup | Merge SqlTypes resource string methodology #3733 are both merged, we'll be in a position to clearly determine which resource strings are truly unused, then to remove them.
2. The minor cleanup of DbReferenceCollection removes the ability to pass a message to the data reader, command or bulk copy associated with a connection whcih is being deactivated. This was never used, and it highlights that DbReferenceCollection and SqlReferenceCollection are simply a list of weak references to those objects. ConditionalWeakTable<TKey, TValue> might now be able to replace the functionality of these classes.

Issues

None, although it follows up from the merge work.

Testing

Automated tests pass, although realistically a simple CI run should validate this.

[paulmedynski]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[benrr101]

Aw man, you're doing all the fun stuff 😝 Thanks for these!