dolt clone -branch should omit remote tracking branches for other branches

[fulghum]

Currently, when you clone a single branch from a Dolt database, you get only that single branch, but you still get remote tracking branches for the other branches in the remote database. To follow Git's semantics, we should not be creating those remote tracking branches for other branches.

[tanyongzhi]

I would like to work on this issue. However, I'm a little confused with the comparison to Git. In Git, a command like git clone -b will also result in remote-tracking branches (viewable using git branch -r) being created. The same behavior happens for Dolt, when we can list the remote-tracking branches using dolt branch -r.

Can you please clarify the expected behavior that the PR resolving this issue should accomplish? Thank you.