message_list: Rename update_group_time_display.
message_list: Rename update_group_time_display.

The name now reflects that this is about date dividers.

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