Remove s3_token functional tests

The s3_token middleware was moved to keystoneclient but the tests
were left to ensure backwards compatibility. The tests have passed
since then and the keystoneclient of the s3_token middleware has
already diverged that causes the tests to fail.

The functional tests are removed and replaced with a test to
ensure that the symbols are forwarded properly.

bp s3-token-to-keystoneclient

Change-Id: Ie1cea741d33400eaa4d4afc7206a3ba1db9a4573