mod: update github.com/russellhaering/gosaml2 to 0.7.0

Created by: unknwon

The PR to merge our changes to the repository of github.com/russellhaering/gosaml2 has been merged, thus we can remove the mod replace to our fork.

The remaining changes are few dependencies updates which are also included in the upstream by other means.

Test plan

Unit tests.

Followup

• Delete our fork: https://github.com/sourcegraph/gosaml2