Remove "OPTIONAL:" from optional argument help text

All arguments starting with '--' are optional and listed
under the 'Optional arguments:' header by argparse.  Remove
the extra note shown for each argument.

Change-Id: Ic361a3bdbd1f1669458e16b99995f0f108400699
Updated from global requirements

Change-Id: I46186b2dc8d0e01bea982b4cab6347bcd86bf558
Merge "Remove "OPTIONAL:" from optional argument help text"