Remove obsolete/deprecated types and methods for RC

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Task description

There are many places where we have an `[Obsolete]` attribute with text like the following: "This method will be removed in 4.8.0 release candidate." We should do a pass to remove these deprecations for our release candidate as indicated by the attribute.

Note that this should ONLY be done once we are ready to proceed to the RC stage; this issue is just for tracking this work so it doesn't get lost. It is not ready to be worked on for a beta release.

Related: #279

When the project is ready for the release-candidate stage, search the C# codebase for [Obsolete] attributes whose messages say they will be removed in the 4.8.0 release candidate. Review the related issue #279 and remove only the deprecated types and methods covered by that criterion; done means those obsolete declarations are removed without applying the work during a beta release.

Written by the indexing model from the issue text.