...given that vnd.sun.star.wfs is long gone.  Note that the old code could have
behaved differently in that for one it could have worked for relative URL input
(as osl_getSystemPathFromFileURL is allowed to accept relative URLs) and for
another could have failed for some file URLs (for which
osl_getSystemPathFromFileURL would return something other than osl_File_E_None
for whatever reason), but it looks plausible to assume that what the call sites
are really interested in is whether a given URL is a file URL.

Simplifies those call sites that already have a INetURLObject instance even
further.

Change-Id: Iaee4595d933a760b8321e42414a9ef0865311833