Revert "Normalize line endings for zulip2.png." (#44)

This reverts commit 6cc9935.

Adding line endings to this PNG broke it.

I noticed this simply because the page generated by zulip-archive showed broken images: 
https://tkf.github.io/zulip-archive-test/stream/259919-tkf/zulip-archive-test/topic/test.20topic.html

Author: tkf