Remove all uses of PhutilGitURI in Phabricator

Summary:
Ref T11137. This class is removed in D16099. Depends on D16099.

PhutilURI now attempts to "just work" with Git-style URIs, so at least in theory we can just delete all of this code and pretend it does not exist.

(I've left "Display URI" and "Effective URI" as distinct, at least for now, because I think the distinction may be relevant in the future even though it isn't right now, and to keep this diff small, although I may go remove one after I think about this for a bit.)

Test Plan:

• Created a new Git repository with a Git URI.
• Pulled/updated it, which now works correctly and should resolve the original issue in T11137.
• Verified that daemons now align the origin to a Git-style URI with a relative path, which should resolve the original issue in T11004.
• Grepped for PhutilGitURI.
• Also grepped in arcanist/, but found no matches, so no patch for that.
• Checked display/conduit URIs.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11137

Differential Revision: https://secure.phabricator.com/D16100