Remove obsolete properties & methods (Part 1)

[peterrsongg]

…etframework and netstandard. Update obsolete methods in commontest projects

Description

This is the first part of a multi-pr effort to remove obsolete properties, methods, and classes from core for v4. This PR address

1. Removing obsolete properties from AWSConfigs and ClientConfig / IClientConfig
2. Refactoring existing integ tests (specifically for clock skews) to not use obsolete properties
3. Make UnmarshallerAsync and sync codepath consistent on when to read the entire response
4. In AssertExtensions.cs, update SHA256 providers to use non-obsolete methods to remove warnings.

Motivation and Context

Testing

Ran the affected integ/unit tests that passed.

Full build of AWSSDK.NetFramework and AWSSDK.NetStandard Solution.

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[normj]

Be sure to update the v4 tracker issue when this is merged. #3362