pgsql: Remove useless configure check

Remove useless configure check

The test for "decltype" as a variant of "typeof" apparently never
worked (see also commit 3582b223d49), so remove it.

Discussion: https://www.postgresql.org/message-id/flat/795b1c54-c64a-47f9-8fa3-880dcab59975%40eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9a8313dabe5ebb6a99d9a165d3c9bc3fa0213088

Modified Files
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config/c-compiler.m4 | 2 +-
configure            | 2 +-
meson.build          | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)