Remove ircd-seven

A future commit will need Chary and its subclasses to use SASL,
but ircd-seven has a different config to use SASL.

And ircd-seven is not used anymore AFAICT, and won't be getting any updates,
so I don't want to bother.

irctest/controllers/ircd_seven.py

@@ -1,12 +0,0 @@
-from typing import Type
-
-from .charybdis import CharybdisController
-
-
-class IrcdSevenController(CharybdisController):
-    software_name = "ircd-seven"
-    binary_name = "ircd-seven"
-
-
-def get_irctest_controller_class() -> Type[IrcdSevenController]:
-    return IrcdSevenController