SDW BP "How to use" section : RIP!

Having re-read the material in this section, and the additional suggestions
given in the wiki page [1], it seems as though almost everything is now
covered elsewhere in the BP doc; the restructuring has helped the document
flow and we have obviously added a lot more material into the document for
the BPs themselves.

So- "How to use" is no more. Gone. Removed. Deleted!

On the plus side, we now have a shorter document without needless
duplication.

Jeremy

[1]:
https://www.w3.org/2015/spatial/wiki/Input_to_%C2%A710_How_to_use_these_best_practices