Remove noise SAL_WARNs that were not warnings, just informative messages

SAL_DEBUG is what should be used for stuff like that (and not committed).

Change-Id: I08505418bf9b55082e0d7672b85f3f76262dbad0
fdo#87030: PDF signing using Windows API, work in progress

Started writing a Windows version of PDFWriterImpl::finalizeSignature(). The
certificate we get from the selection dialog (in xmlsecurity) is from the
Windows built-in store anyway, so it is pointless to try to use it with
NSS. (See bug for longer discussion.)

So far it was pretty straightforward. The WinCrypt API seems clean and easy to
use. But for some reason the CryptSignHash() call fails with "Keyset does not
exist" (NTE_BAD_KEYSET). What am I missing?

Anyway, comitting this now as it does compile and doesn't make things worse.

Change-Id: I0941995ad6e22c5487c6e6fe0084d3df0b2341c7