Remove jarring viewer log spam message -- unless it's true.

For as long as I've been paying attention to viewer logs, every run has always
stated -- in all-caps, no less! :
NOTE: ALL NOTIFICATIONS THAT OCCUR WILL GET ADDED TO IGNORE LIST FOR LATER RUNS.
I have always found that unsettling, having little desire to automatically
ignore notifications -- especially not whatever random set happens to manifest
during a particular run. However, over time I've learned that it seems to have
no actual impact. I've wondered (not too hard) what it actually *does* mean --
but generally I'm looking at a viewer log because I'm in hot pursuit of some
quite different problem.
Stumbling across the source for this message today in
LLViewerWindow::LLViewerWindow, I was shocked -- shocked! -- to find it was
being produced unconditionally! Therefore it has heretofore been utterly
meaningless log spam. It provided no additional information whatsoever to
anyone reading a log -- only that vague sense of unease.
Make this conditional on gSavedSettings.getBOOL("IgnoreAllNotifications"),
which would appear to be the original intent. Now its presence (or absence)
actually says something about internal conditions in the viewer.