preinst is in libasound2 1.0.25-1ubuntu10.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 | #!/bin/sh
set -e
dpkg-maintscript-helper rm_conffile /etc/ld.so.conf.d/libasound2.conf 1.0.24.1-0ubuntu6 -- "$@"
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