default stream groups: Fix buggy LDAP behavior.
default stream groups: Fix buggy LDAP behavior.

With LDAP authentication, we don't currently have a good way to
support the default stream groups feature.

The old behavior was just to assume a user select every default stream
group, which seems wrong; since we didn't prompt the user about these,
we should just ignore the feature.

punchagan/zulip,showell/zulip,eeshangarg/zulip,showell/zulip,shubhamdhama/zulip,zulip/zulip,timabbott/zulip,hackerkid/zulip,eeshangarg/zulip,hackerkid/zulip,eeshangarg/zulip,timabbott/zulip,timabbott/zulip,rht/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,brainwane/zulip,synicalsyntax/zulip,punchagan/zulip,showell/zulip,zulip/zulip,kou/zulip,brainwane/zulip,andersk/zulip,shubhamdhama/zulip,synicalsyntax/zulip,zulip/zulip,shubhamdhama/zulip,punchagan/zulip,zulip/zulip,shubhamdhama/zulip,kou/zulip,brainwane/zulip,timabbott/zulip,timabbott/zulip,andersk/zulip,hackerkid/zulip,kou/zulip,hackerkid/zulip,brainwane/zulip,andersk/zulip,andersk/zulip,synicalsyntax/zulip,eeshangarg/zulip,synicalsyntax/zulip,punchagan/zulip,eeshangarg/zulip,shubhamdhama/zulip,rht/zulip,rht/zulip,kou/zulip,showell/zulip,eeshangarg/zulip,kou/zulip,synicalsyntax/zulip,showell/zulip,rht/zulip,punchagan/zulip,hackerkid/zulip,hackerkid/zulip,kou/zulip,brainwane/zulip,zulip/zulip,synicalsyntax/zulip,shubhamdhama/zulip,andersk/zulip,rht/zulip,kou/zulip,shubhamdhama/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,andersk/zulip,brainwane/zulip,rht/zulip,timabbott/zulip,synicalsyntax/zulip,brainwane/zulip,showell/zulip,punchagan/zulip,timabbott/zulip,showell/zulip,zulip/zulip