ssh: drop unused variable from model

The SSHModel contained a ssh_import_id member variable. According to the
comment, it was originally meant to store meta-data about a SSH key ;
and was supposed to allow showing some sort of info back in the SSH view
if the user decides to go back.

I suspect that this variable has been unused for a long time.
Furthermore, it can only hold information about a single SSH key and we
support multiple keys..

Let's get rid of it.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/models/ssh.py

@@ -26,10 +26,6 @@ class SSHModel:
         self.install_server = False
         self.authorized_keys: List[str] = []
         self.pwauth = True
-        # Although the generated config just contains the key above,
-        # we store the imported id so that we can re-fill the form if
-        # we go back to it.
-        self.ssh_import_id = ""
 
     async def target_packages(self) -> List[TargetPkg]:
         if not self.install_server: