options: remove stale comment

Fixes:		ea916b6 ("Remove TCP_SAD optional code now that the sack filter performs this function.")
Sponsored by:	Netflix, Inc.

Author: tuexen

sys/conf/options

@@ -235,11 +235,6 @@ TCP_REQUEST_TRK opt_global.h
 TCP_ACCOUNTING	opt_global.h
 TCP_BBR		opt_inet.h
 TCP_RACK	opt_inet.h
-#
-# TCP SaD Detection is an experimental Sack attack Detection (SaD)
-# algorithm that uses "normal" behaviour with SACK's to detect
-# a possible attack. It is strictly experimental at this point.
-#
 TURNSTILE_PROFILING
 UMTX_PROFILING
 UMTX_CHAINS	opt_global.h