pgsql: Remove remaining references to version-0 calling convention ind

Remove remaining references to version-0 calling convention in docs.

Support for version-0 calling convention was removed in PostgreSQL v10.
Change the SPI example to use version 1 convention, so that it actually
works.

Author: John Naylor
Discussion: https://www.postgresql.org/message-id/CAJVSVGVydmhLBdm80Rw3G8Oq5TnA7eCxUv065yoZfNfLbF1tzA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f66912b0a0387aab5f5bbcd9d56ab92200395d2e

Modified Files
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doc/src/sgml/plhandler.sgml |  5 ++---
doc/src/sgml/spi.sgml       | 18 +++++++-----------
2 files changed, 9 insertions(+), 14 deletions(-)