address: Remove dead msg_type function.
address: Remove dead msg_type function.

This was never used; we instead use `.is_stream` and `.is_private`
instead.

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