mediawiki.action.edit.js: Remove WikiEditor iframe hack from 2010

Introduced in aa69029e2 (r62242) by Roan.

The iframe this refers to is going away for good in I2d736911.

Change-Id: If2f225c51791b46e25468deb4081ecac67db409a
Merge "mediawiki.action.edit.js: Remove WikiEditor iframe hack from 2010"