Remove System.Text.Json and System.Text.RegularExpressions

[frederikprijck]

Changes

Both dependencies are not used explicitly and were added a while ago to fix a snyk vulnerability. As those pinned versions are no longer supported, we removing them and relying on the versions used by our direct dependencies that need them.

Checklist

• [x] I have read the Auth0 general contribution guidelines
• [x] I have read the Auth0 Code of Conduct
• [x] All existing and new tests complete without errors
• [x] All code guidelines in the CONTRIBUTING documentation have been run/followed