update: Remove images as they are successfully flashed

Remove image files as they are flashed so a repeated call to
update does not erase and write the image again.

As we add the ability to call update at runtime repeated calls
are expected.  This both signals successful copy and removes the
need for callers to cleanup.

Also remove commented alternate flash method using eraseall
that was not tested.

Signed-off-by: Milton Miller <miltonm@us.ibm.com>
diff --git a/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-update.sh b/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-update.sh
index 6b0d7a0..edaf195 100755
--- a/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-update.sh
+++ b/common/recipes-phosphor/obmc-phosphor-initfs/files/obmc-update.sh
@@ -138,8 +138,7 @@
 do
 	m=$(findmtd ${f#$image})
 	echo "Updating ${f#$image}..."
-	# flasheraseall /dev/$m && dd if=$f of=/dev/$m
-	flashcp -v $f /dev/$m
+	flashcp -v $f /dev/$m && rm $f
 done
 
 if test "x$toram" = xy