Don't tell user about reloading microdesc cache at startup

Sep 03 18:12:41.000 [notice] Reloaded microdescriptor cache.  Found 0 descriptors.

is there on initial startup every time.

If you've already got lots of dir info, it would say e.g.

Sep 03 18:24:41.000 [notice] Reloaded microdescriptor cache.  Found 3035 descriptors.

Our bootstrap warnings are supposed to tell the user when there's a problem, and our bootstrap notices say when there isn't. We don't need this extra line.

I had originally thought to do a fancier fix like:

-  log_notice(LD_DIR, "Reloaded microdescriptor cache.  Found %d descriptors.",
-             total);
+  log(total ? LOG_NOTICE : LOG_INFO, LD_DIR,
+      "Reloaded microdescriptor cache. Found %d descriptors.", total);

but then I noticed that 0.2.2.38 doesn't have a line about loading descriptors, so I have tentatively marked this as 0.2.3.x-final and suggest just downgrading the log message.