JDK-8175825 Stop including pubs repo

[Magnus Ihse Bursie]

Here are some externally visible changes for an internal change: we will 
stop copying documentation from the "pubs" repo, and some of that logic 
has leaked through into the open parts, and will be removed with this patch.

I have also renamed Javadoc.gmk to Docs.gmk to better fit the current 
purpose, and included some other minor cleanups.

Bug: https://bugs.openjdk.java.net/browse/JDK-8175825
WebRev: http://cr.openjdk.java.net/~ihse/JDK-8175825-no-more-pubs/webrev.01

/Magnus