Makefile: DESTDIR should be stripped from config files location during linking

[joebonrichie]

Otherwise we get:

$ sudo usysconf run -d
 ✚  Started usysconf
 ✚  Falling back to rigorous check for chroot
 ✚  Skipped directory '/home/build/YPKG/root/usysconf/install/etc/usysconf.d':
 ✚      Not found.
 ✚  Skipped directory '/home/build/YPKG/root/usysconf/install/usr/share/default/usysconf.d':
 ✚      Not found.
 ✚  Skipped directory '/home/ninya/.config/usysconf.d':
 ✚      Not found.
 🕱  No triggers available

minor issue; workaround is to build and install separately instead of install step with DESTDIR= passed doing the building.