Remove Pragma Disable Warning For New ValidateTokenAsync Method on Saml2TokenHandler

[FuPingFranco]

Due to the TDD approach we are taking on constructing the new ValidateTokenAsync method on Saml2TokenHandler that implement our new token validation model, we introduced pragma warnings disable around methods that passed CancellationToken. We should be able to remove them once we get into async validators such as the Issuer validator.

[iNinja]

This will be solved once #2929 is merged.