We remove the secondary unique column sshUserName and store it in
the AccountExternalId entity instead. This change is necessary to
support databases which do not allow mulitiple key attributes for
an entity.
Change-Id: I20076a05f2ea083da6044a4f1ed2f0672e85739a
Signed-off-by: Shawn O. Pearce <sop@google.com>
f2bab2afc9