minor: Avoid recip.user_id defensive fallback.
minor: Avoid recip.user_id defensive fallback.

The recip.id || recip.user_id idiom has only been
needed for some old unit tests.

It was previously required as a bad workaround for the
local echo issue fixed in dd1a6a97bdac0fc70422c74a82c4cbd268be6eff 
where we would get `display_recipient` values added in an invalid format.
synicalsyntax/zulip,zulip/zulip,rht/zulip,hackerkid/zulip,timabbott/zulip,zulip/zulip,punchagan/zulip,brainwane/zulip,hackerkid/zulip,punchagan/zulip,showell/zulip,andersk/zulip,synicalsyntax/zulip,shubhamdhama/zulip,kou/zulip,synicalsyntax/zulip,timabbott/zulip,showell/zulip,shubhamdhama/zulip,andersk/zulip,punchagan/zulip,showell/zulip,timabbott/zulip,showell/zulip,showell/zulip,rht/zulip,andersk/zulip,punchagan/zulip,andersk/zulip,timabbott/zulip,synicalsyntax/zulip,shubhamdhama/zulip,andersk/zulip,andersk/zulip,shubhamdhama/zulip,hackerkid/zulip,zulip/zulip,brainwane/zulip,eeshangarg/zulip,showell/zulip,synicalsyntax/zulip,synicalsyntax/zulip,andersk/zulip,rht/zulip,rht/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,timabbott/zulip,zulip/zulip,zulip/zulip,brainwane/zulip,rht/zulip,kou/zulip,shubhamdhama/zulip,hackerkid/zulip,hackerkid/zulip,punchagan/zulip,timabbott/zulip,kou/zulip,shubhamdhama/zulip,eeshangarg/zulip,brainwane/zulip,timabbott/zulip,kou/zulip,kou/zulip,showell/zulip,hackerkid/zulip,rht/zulip,synicalsyntax/zulip,eeshangarg/zulip,shubhamdhama/zulip,brainwane/zulip,eeshangarg/zulip,eeshangarg/zulip,brainwane/zulip,zulip/zulip,rht/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,brainwane/zulip,eeshangarg/zulip