Remove dependency credential test.

[robdimsdale]

• With the change to the CFF-owned CDN, it no longer supports the use case of credentials in the dependency URL. So this test fails for environmental reasons.
• Given that this CDN is how consumers get their depedencies, and hence the entire feature no longer works for CFF consumers, it is reasonable to drop the test rather than try to find an alternative dependency store that accepts credentials.
• Phrased another way - even if we find a way to fix the test, the behavior it validates is not something consumers can use. So it is better to drop the test.