[Router] Remove XApp token once we have an OAuth token.
[Router] Remove XApp token once we have an OAuth token.

This may have been leading to some users getting 401
responses from the API if after a week the XApp token they
were still including was no longer valid.

So hopefully fixes: https://sentry.io/artsynet/eigen/issues/283607999/

artsy/eigen,artsy/eigen,artsy/eigen,artsy/eigen,artsy/eigen,artsy/eigen,artsy/eigen