Cleaning up old shared libraries on NetBSD
NetBSD has a focus of maintaining binary compatibility. And so, during system upgrades, system shared libraries with old major numbers are left installed. Old minor versions are cleaned up via postinstall(1). If you wish to remove old major version libraries, a script is present in the NetBSD source repository for doing this:
/usr/src/lib/checkoldver /usr/lib | xargs rm -f
Note that this may break third party binaries, including pkgsrc binaries.