Revert "iotests: Stop NBD server in test 162 before starting the next one"

This reverts commit e2668ba1ed.

This commit made test 162 fail occasionally with:

 162   fail      [13:06:40] [13:06:40]   0.2s   (last: 0.2s)  output mismatch
 --- tests/qemu-iotests/162.out
 +++ tests/qemu-iotests/scratch/qcow2-file-162/162.out.bad
 @@ -3,6 +3,7 @@
  === NBD ===
  qemu-img: Could not open 'json:{"driver": "nbd", "host": -1}': address
   resolution failed for -1:10809: Name or service not known
  image: nbd://localhost:PORT
 +./common.rc: line 371: kill: (891116) - No such process
  image: nbd+unix://?socket=42

The nbd server should normally terminate automatically, so trying to
kill it here now seems to cause a race that will cause a test failure
when the server terminated before the kill command has been executed.

The "Stop NBD server" patch has originally been written to solve another
problem with a hanging nbd server, but since that problem has been properly
solved by commit 3e16834856, we now don't need the "_stop_nbd_server" here
anymore.

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250326143533.932899-1-thuth@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

tests/qemu-iotests/162

@@ -65,7 +65,6 @@ done
 
 $QEMU_IMG info "json:{'driver': 'nbd', 'host': 'localhost', 'port': $port}" \
     | grep '^image' | sed -e "s/$port/PORT/"
-_stop_nbd_server
 
 # This is a test for NBD's bdrv_refresh_filename() implementation: It expects
 # either host or path to be set, but it must not assume that they are set to