Inline get_recipient_user_ids() into two callers.
Inline get_recipient_user_ids() into two callers.

This sets us up a subsequent commit where we need more data
from the Subscription table to build recipient info, so the
function boundary doesn't work any more for get_recipient_info,
which is part of the heavily optimized send-message
path.

We used to share code here with typing notifications, but
typing notifications need a lot less data than the
send-message path, so it's useful to decouple these two
things.  The idioms that are duplicated here are pretty simple
one-liners.

mahim97/zulip,zulip/zulip,jackrzhang/zulip,rht/zulip,brockwhittaker/zulip,kou/zulip,timabbott/zulip,andersk/zulip,amanharitsh123/zulip,andersk/zulip,showell/zulip,amanharitsh123/zulip,brainwane/zulip,Galexrt/zulip,mahim97/zulip,dhcrzf/zulip,brainwane/zulip,verma-varsha/zulip,timabbott/zulip,hackerkid/zulip,shubhamdhama/zulip,hackerkid/zulip,shubhamdhama/zulip,verma-varsha/zulip,rishig/zulip,rishig/zulip,mahim97/zulip,dhcrzf/zulip,jackrzhang/zulip,showell/zulip,tommyip/zulip,showell/zulip,punchagan/zulip,verma-varsha/zulip,rht/zulip,kou/zulip,rishig/zulip,punchagan/zulip,zulip/zulip,showell/zulip,amanharitsh123/zulip,Galexrt/zulip,mahim97/zulip,hackerkid/zulip,Galexrt/zulip,punchagan/zulip,amanharitsh123/zulip,synicalsyntax/zulip,jackrzhang/zulip,punchagan/zulip,kou/zulip,tommyip/zulip,andersk/zulip,tommyip/zulip,verma-varsha/zulip,timabbott/zulip,brockwhittaker/zulip,amanharitsh123/zulip,rht/zulip,synicalsyntax/zulip,kou/zulip,timabbott/zulip,dhcrzf/zulip,dhcrzf/zulip,andersk/zulip,brainwane/zulip,brainwane/zulip,rht/zulip,hackerkid/zulip,timabbott/zulip,jackrzhang/zulip,brainwane/zulip,shubhamdhama/zulip,dhcrzf/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,jackrzhang/zulip,hackerkid/zulip,rht/zulip,brockwhittaker/zulip,punchagan/zulip,jackrzhang/zulip,brockwhittaker/zulip,hackerkid/zulip,rishig/zulip,synicalsyntax/zulip,synicalsyntax/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,mahim97/zulip,punchagan/zulip,timabbott/zulip,zulip/zulip,dhcrzf/zulip,amanharitsh123/zulip,verma-varsha/zulip,verma-varsha/zulip,timabbott/zulip,kou/zulip,rishig/zulip,showell/zulip,tommyip/zulip,eeshangarg/zulip,Galexrt/zulip,showell/zulip,dhcrzf/zulip,rht/zulip,andersk/zulip,Galexrt/zulip,shubhamdhama/zulip,showell/zulip,jackrzhang/zulip,brainwane/zulip,rishig/zulip,eeshangarg/zulip,eeshangarg/zulip,Galexrt/zulip,andersk/zulip,eeshangarg/zulip,shubhamdhama/zulip,punchagan/zulip,tommyip/zulip,rht/zulip,hackerkid/zulip,brockwhittaker/zulip,synicalsyntax/zulip,synicalsyntax/zulip,brockwhittaker/zulip,zulip/zulip,mahim97/zulip,synicalsyntax/zulip,tommyip/zulip,Galexrt/zulip,shubhamdhama/zulip,andersk/zulip,tommyip/zulip,rishig/zulip,shubhamdhama/zulip,eeshangarg/zulip,brainwane/zulip