maintenance: Deprecate Maintenance::hasArg/getArg with no param

maintenance: Deprecate Maintenance::hasArg/getArg with no param

Benefit of keeping the parameter optional:
- In maintenance scripts that really only have one parameter, it's a
  little more convenient to be able to ask for *the* parameter via an
  empty getArg().

Disadvantages:
- It's unclear what getArg() means when there is no indication *which*
  argument the code asks for. This might as well return the last
  argument, or an array of all arguments.
- In scripts with two or more arguments, it's confusing to see
  getArg( 1 ) next to an empty getArg().
- The methods are more complex and a bit more complicated to use with
  the extra feature of this parameter being optional. Users need to
  look up what the default is to be able to use it safely.

Change-Id: I22a43bfdfc0f0c9ffdb468c13aba73b888d1f15e