presence: Document why we no longer need suspect_offline.
presence: Document why we no longer need suspect_offline.

Since it took a lot of effort to debug the original issue that caused
us to introduce suspect_offline, it seems worth writing a comment
explaining why we won't see that issue here.

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