Revert "Add instagram.com" as it's duplicated.

There are same rules in `gfwlist.txt` now. :grinning: 
See https://code.google.com/p/autoproxy-gfwlist/issues/detail?id=161

This reverts commit https://github.com/Wllmw/GFWListPlus/commit/3477fb3f39ae85f9ce513f9d501044d103be27d8 .