pgsql: Don't try to import a non-exported object in vcregress.pl

Don't try to import a non-exported object in vcregress.pl

Commit ca9e9b08e453 wrongly tried to import devnull from File::Spec, but
it's not exported, you just call the method via the class. This was
harmless until modern perls complained, so stop doing that.

Per buildfarm failures.

Backpatch 14 thru 16

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b31fa1f87f373d8d2fdc43a489ef5611de7a2af7

Modified Files
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src/tools/msvc/vcregress.pl | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)