Correct location of AmazonS3 command line client

This code belongs inside of the org.eclipse.jgit.pgm bundle
so it is executable from the command line.

In af5cb5ced938 ("Move AmazonS3 command line utility to jgit-pgm")
I accidentally moved this class into the wrong directory, probably
during some sort of rebase when I tried to pull this commit out of
its original position in an abanonded Maven refactoring series.

Change-Id: I19adafa87b70586dd44040e9dfce30f3d482ed28
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>