DOC:  Remove documentation that is not relevant to VTK6

This readme file does not work for VTK6 and is very confusing.

Change-Id: If4b03ae5b5bfe03c488a11c1519c0b2f9dfa4374
Merge topic 'RemoveOutdatedREADME' into master

ddd94976 DOC:  Remove documentation that is not relevant to VTK6