Remove obsolete datestamp comment
Disable Bio-Formats update checker

This change has two effects:

1) The "Plugins > LOCI > Update LOCI Plugins" command now simply
   launches the ImageJ updater.

2) The check for a new Bio-Formats stable release is now disabled upon
   each startup of Fiji. While it is possible to reenable it for the
   lifetime of the JVM using the "Plugins > LOCI > LOCI Plugins
   Configuration" dialog, this change will catch the vast majority of
   undesirable update checks.