Clean up the "installdirs" target in Makefile.in
The isc-config.sh script was removed in 2019 [1], so the top-level Makefile does not need to create ${bindir} and ${mandir}/man1 any more.
All named options creating files in the ${localstatedir}/run/named directory are able to automatically create that directory (as well as its containing directories), so there is no need for the top-level Makefile to create ${localstatedir}/run.
Clean up the "installdirs" target in the top-level Makefile accordingly.
[1] see commit 4b44351e
Closes #2709 (closed)