gpstime: update to use system tzdata leap-seconds.list file

rather than one maintained by the now-deprecated ietf-leap-seconds package.

src/drv/gpstime/calc_gps_offset/calc_gps_offset.py

@@ -139,7 +139,7 @@ for the LIGO gpstime driver.""")
     help_txt = "Calculate offset where there is no IRIG-B signal"
     parser.add_argument("-s", "--system-time", help=help_txt,
                         action="store_true", default=False)
-    default = "/var/cache/ietf-leap-seconds/leap-seconds.list"
+    default = "/usr/share/zoneinfo/leap-seconds.list"
     help_txt = "Location of a leap-second database [{0}]".format(default)
     parser.add_argument("-l", "--leap-second-db", help=help_txt,
                         default=default)