Don't package /var/db/locate.database

... or install an empty file.

The locate database is a mutable working file, and unsuitable to be
managed by pkg(8). locate(1) copes gracefully with the absence of
this file. Running /etc/periodic/weekly/310.locate will create the
locate database with the correct ownership and permissions.

Having the locate.database file as part of the FreeBSD-runtime package
means it gets zeroed if ever that package gets updated, which is
excessive, given that updating packages will typically only change a
relatively small number of the _filenames_ on the system -- unlike the
file contents. Plus it always causes it to flag as modified when
verifying checksums, but /var/db/locate.database is expected to be
modified by the user.

MFC after: 1 week
Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D45384

(cherry picked from commit 4354163e5fe8e180f62b892cdc3e51e3d7e4706f)