NetBSD compat shims in rc.subr

[Ed Maste]

On Mon, Jan 25, 2010 at 12:46:05PM -0800, Doug Barton wrote:

> Oh, one caveat JIC, please grep through /etc and make sure the variables
> you're removing aren't used by something.

I found that OSTYPE wasn't used in etc/ beyond the case statement(s) in
rc.subr itself, so removed it.

Some rc.d scripts use SYSCTL_W so I left it alone (fixed to the FreeBSD
case):

> >> +SYSCTL_W="${SYSCTL}"

-Ed