presence: Remove obsolete defensive code.
presence: Remove obsolete defensive code.

If you look at info_for, it clearly never returns
`undefined`, so this defensive code isn't preventing
any bugs.

Also, we are doing a better job now of filtering
user_ids in upstream code.

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