Tweaked the wording for LDP-RS HTTP PUT to be apply to LDPRs

The previous clauses for LDR PUT were written before we had separate
concepts for LDP-RS and LDP-NR.  They are generally applicable to LDP-NRs,
so I left them in the general LDPR HTTP PUT section [1] and improved on the
language to remove a few RDF-specific words.

[1] - https://dvcs.w3.org/hg/ldpwg/raw-file/default/ldp.html#ldpr-HTTP_PUT

- Steve Speicher