lalapps: backport 53a34327 to release branch
commit 53a3432709fac355b9b25b9c0f41ba4f372347d7
Author: Duncan Macleod <duncan.macleod@ligo.org>
Date: Thu Dec 12 18:54:59 2019 +0000
lalapps: use LALPULSAR_DATADIR instead of LALPULSAR_PREFIX
simplifies things a bit