zilencer: Make /billing appear without i18n prefix.
zilencer: Make /billing appear without i18n prefix.

This copies what we do in `zproject/urls.py` for pages in the
main Django app.

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