comms/chu: Simplify port by eliminating custom extraction target
The default extract target can be used if NO_WRKSUBDIR is set. The
only unique command is the gunzip, which works well as a post-extract
target. This eliminates the undefined use of EXTRACT_CMD to ensure
the port keeps working in the future.
CHU is a time-standard shortwave radio station operated by National
Research Council Canada (NRC). This software uses signals from radio
station CHU to set and frequency discipline the system clock on a
Linux (FreeBSD) based system.
Submitted by: Diane Bruce <db(at)db.net>