upgrade: Remove disused hack for `zulip-dropbox.png`.
upgrade: Remove disused hack for `zulip-dropbox.png`.

I believe this hack is no longer being triggered; so cut it out.

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