refactor: Remove obsolete .message-pane.
refactor: Remove obsolete .message-pane.

This is an obsolete css class in zulip.css.

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