issues customizing C stuff

[Dave Love]

1. I think CC mode should have its own Custom group.  Currently in a
   customization buffer for a cc-mode variable, going up to the parent
   group sucks in hideif, cpp and cmacexp, which is infelicitous.

2. More importantly, going to the parent group (`c') loads c-mode --
   the obsolete one.  That definitely shouldn't be loaded, as the
   comment on its defgroup says.  If cc-mode is already loaded when
   you do this, `c-mode' becomes the wrong thing entirely.

   I couldn't immediately spot why c-mode.elc gets loaded.  Perhaps it
   should just be junked.