Remove the now pointless sign in callback support

Since 577257935975f38899a26021e328c8c48c3a7c00 "Never place an OpenID
provider into an iframe" we no longer support invoking an application
supplied callback upon login success, as the page is reloaded during
the redirect back from the OpenID provider.  To do state restore we
need something more complex than just an implementation of a Java
interface, like storing string data into a cookie.

As the only real user was the abstract patch table, to create an
editor on the line you double clicked, and that hasn't worked since
the change, we can rip out a good chunk of complex code and make it
a whole lot simpler in the process.

Signed-off-by: Shawn O. Pearce <sop@google.com>
5 files changed