people: Simplify people.get_recipient_count.
people: Simplify people.get_recipient_count.

Once we get past the special check for fake
person objects already having `pm_recipient_count`,
we can rely on the object being a `person`
object with `user_id` set.

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