Remove/address usage of `TestScopedEnvironmentVariable`

We should remove all usages of https://github.com/Azure/azure-functions-host/blob/dev/test/WebJobs.Script.Tests.Shared/TestScopedEnvironmentVariable.cs

Usage of this class is problematic as it still sets these variables for all other tests running concurrently.

If usage of this class **MUST** remain, then all tests using it need to be added to a collection to avoid running concurrently.

Start by inspecting test/WebJobs.Script.Tests.Shared/TestScopedEnvironmentVariable.cs and searching the test suite for every usage. Determine whether each usage can be removed or whether the affected tests must share a collection to prevent concurrent execution. Done means the class has no usages, or all remaining users are grouped to avoid running concurrently.

Written by the indexing model from the issue text.