Refactor Rebase to use PatchSetInserter

Refactor the rebase to use the PatchSetInserter class.

The PatchSetInserter takes care of sending email notifications about
new patch sets, so remove the rebase-specific sender.

Change-Id: I1e05db299d03d6b4a9eec4ae5bca4cd62cf01a4f
7 files changed