[amber] Revert "[amber] use the configured transport with oauth2"

This reverts commit 9d839ff7d804ce5702c271d46d7cca9a66fc84a8. The oauth
wrapper uses the provided transport anyway, and replacing it disables
the oauth token injection.

Test: manual

Change-Id: I56d0dd1841b434aad9ca5df9b9d4e904c58c4300
1 file changed