zerver/tornado: remove `import six`.
zerver/tornado: remove `import six`.

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