Remove duplicated --schema option for tenant_command

Maybe I misunderstand something, but it looks like '--schema' is added twice to option list for 'tenant_command' command line argument: first in  `management/commands/__init__.py` (in the constructor for InteractiveTenantOption) and then once again in `management/commands/tenant_command.py`.

This causes `optparse.OptionConflictError: option -s/--schema: conflicting option string(s): -s, --schema` on my machine while running basic `./manage.py tenant_command createsuperuser`.