Refactor code to hide APIs that are not relevant for managed identity. For more information see design doc

Refactor the code to hide APIs not supported for managed identity. For more information see [design doc](https://identitydivision.visualstudio.com/DevEx/_git/AuthLibrariesApiReview?path=/ManagedIdentity/ManagedIdentity.md&_a=preview&anchor=msal-apis-that-should-either-be-disabled-or-no-op-with-managed-identity).
