Fix gpexpand help usage
In commit the --novacuum option is removed, however the help
page of gpexpand keep the -V option, which is a short option for
novacuum.
@@ -93,7 +93,7 @@ Remaining TODO items:
_usage = """[-f hosts_file]
-gpexpand -i input_file [-B batch_size] [-V] [-t segment_tar_dir] [-S]
+gpexpand -i input_file [-B batch_size] [-t segment_tar_dir] [-S]
gpexpand [-d duration[hh][:mm[:ss]] | [-e 'YYYY-MM-DD hh:mm:ss']]
[-a] [-n parallel_processes]
