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_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/10f087987741394254323bf0016ad1d631494a3d

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