Remove Godeps; deps are vendored in diego-release

[#78292566]

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>
Remove concourse support

To postpone figuring out how to make this work with our new approach of vendoring deps in diego-release

[#78292566]

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>