Remove the pointless GitProjectData resource change listener

Remove the pointless GitProjectData resource change listener

Apparently on any IResourceChangeEvent.POST_CHANGE we just burn some
CPU time and generate some garbage for the GC to clean out later.  I
cannot see a reason why this code is still here.  My memory says we
did this in the past to notify the resource decorator that it needs
to update, or we used it for our cache tree invalidation.

Since this code has no side effect other than to waste time we can
safely remove it, and cut our project down a little bit.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>