[Extensions] Remove local VersionOverrides

[jsquire]

Problem Statement

As part of the fix for #48368, tests were added to the Microsoft.Azure.Extensions package which rely on the 8.x version of the ASP.NET Core testing packages. Because the central version of Microsoft.AspNetCore.Mvc.Testing is used in several other projects and is very old, it will be included in the repository-wide efforts to bump dependencies to the 8.x range and a local override will be used for the extensions.

Scope of work

• Once the central version of Microsoft.AspNetCore.Mvc.Testing has been updated to the 8.x line, remove the local override in the Microsoft.Extensions.Azure.Tests project.

Success criteria

• The local override has been removed and tests continue to pass reliably.

[jsquire]

//fyi: @m-redding