Partially revert r367756 (chpass(1) synopsis changes)

Let's have two entries in the synopsis:
- chpass now lists options which can be used for a non-NIS-specific
  functionalities.
- ypchpass lists all the options of chpass + the NIS-specific ones.

Technically, it is an artificial distinction, as chpass and ypchpass behave
identicaly. Nevertheless, it might help navigating the synopsis section.