popovers: Refactor showmessage_info_popover.
popovers: Refactor showmessage_info_popover.

We now rely on getting the sender object from people.js, rather than
hackishly trying to handle the case that it doesn't exist.

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