pgsql: Improved ECPG warning as suggested by Michael Paquier and remove

Improved ECPG warning as suggested by Michael Paquier and removed test case
that triggers the warning during regression tests.

Branch
------
REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e2d6da0708df2c2e244d8748c26ebc49c0963ed5

Modified Files
--------------
src/interfaces/ecpg/preproc/ecpg.header            |   3 +-
src/interfaces/ecpg/test/expected/sql-declare.c    | 185 +++++++--------------
.../ecpg/test/expected/sql-declare.stderr          | 150 ++++++-----------
.../ecpg/test/expected/sql-declare.stdout          |   6 +-
src/interfaces/ecpg/test/sql/declare.pgc           |  37 +----
5 files changed, 118 insertions(+), 263 deletions(-)