Further cleanup for commit 54cd6fc83.

Further cleanup for commit 54cd6fc83.

Commit 54cd6fc83 set the version argument for the stats-import functions
introduced by that commit, which is of type int, using UInt32GetDatum,
not Int32GetDatum.  This would be completely harmless as it's positive
and currently ignored in the functions, but let's fix that code to use
Int32GetDatum for consistency.

Author: Etsuro Fujita <etsuro.fujita@gmail.com>
Discussion: https://postgr.es/m/CAPmGK14aremJGrPezVwFqWt7dnrMhD3KF1DgzsRygAUPETBU7w%40mail.gmail.com
Backpatch-through: 19