Remove builtins imports

This module is not intended to be used directly in most cases, per:
https://docs.python.org/3/library/builtins.html

None of our usages warrant the explicit import. We also avoid some
confusion as folks dig to see what we are doing to require
importing builtins directly.

evennia/server/serversession.py

@@ -6,8 +6,6 @@ connection actually happens (so it's the same for telnet, web, ssh etc).
 It is stored on the Server side (as opposed to protocol-specific sessions which
 are stored on the Portal side)
 """
-from builtins import object
-
 import weakref
 import time
 from django.utils import timezone