pgsql: Revert ECPG's use of pnstrdup()

Revert ECPG's use of pnstrdup()

Commit 0b9466fce added a dependency on fe_memutils' pnstrdup() inside
informix.c. This adds an exit() path in a library, which we don't
want. (Unlike libpq, the ecpg libraries don't have an automated check
for that, but it makes sense to keep them to a similar standard.) The
ecpg code can already handle failure results from the *strdup() call
by itself.

Author: Jacob Champion <jacob(dot)champion(at)enterprisedb(dot)com>
Discussion: https://www.postgresql.org/message-id/CAOYmi+=pg=W5L1h=3MEP_EB24jaBu2FyATrLXqQHGe7cpuvwyg@mail.gmail.com

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ee2997c678d86568328f0221717676f86b8aa6f6

Modified Files
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src/interfaces/ecpg/compatlib/informix.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)