headsup on enclosure driver

[Matthew Jacob]

Doing two things:

1) Removing SEN support. I doubt any of the hardware survived past 1996 
and I'll put the code back and eat my freebsd membership card if I'm 
wrong. It wasn't supported anyway.

2) Default logging via enc_log to not be chatty unless a new sysctl 
enc_verbose or bootverbose is set.
This is all motivated by my hudson case system's log that is filled full 
of charm like:

ses0: Element 6 Beyond End of Additional Element Status Descriptors

Will hold off checking in for a day in case anyone cares.