R1:839f3df9c262

Stop trasforming "scp-style" URIs into normal URIs in Git

Summary:
See D3033, T1529. We currently transform "scp-style" `user@host:path` URIs into normal `ssh://user@host/path` URIs. This is undesirable for two reasons:

- The paths aren't always equivalent. They are for GitHub, which is why I missed this originally, but in the general case the ":path" is resolved relatively and the "/path" is resolved absolutely. So this transformation can break things.
- It confuses users, who do not think of…