import: Fix re-rendering of markdown for Zulip->Zulip imports.
import: Fix re-rendering of markdown for Zulip->Zulip imports.

The code added in 26300110cae4e1bc3f0d95f974b3357074220acf was only
needed for importing data from Slack, Gitter, or another tool which
doesn't use Zulip's markdown format.

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