[wp-docs] Version specific banners for Codex

[Lorelle VanFossen]

I firmly have believed from the beginning that inclusion of the version 
in the title or section, or highlighted in bold within an article, is 
good enough and the banners are not necessary, except on specific pages 
such as Install or Upgrade, IF the issue is directly related to version 
specifics. It makes it easier to scan down the list for "my" version. I 
personally do not want the use of the banner templates to be spread all 
over the Codex, but used lightly and with a very specific intention.

I've updated the example page accordingly, to add clarification.

Kaf, and others still thinking this way:  As long as the thinking 
continues to be "upgrade or be deprecated", implying there is little 
choice in the matter as you will be better off with upgrading, version 
specific manuals are not in the offering. One manual - all versions.

Lorelle