pgsql: Doc: improve documentation about ORDER BY in matviews.

Doc: improve documentation about ORDER BY in matviews.

Remove the confusing use of ORDER BY in an example materialized
view.  It adds nothing to the example, but might encourage
people to follow bad practice.  Clarify REFRESH MATERIALIZED
VIEW's note about whether view ordering is retained (it isn't).

Maciek Sakrejda

Discussion: https://postgr.es/m/CAOtHd0D-OvrUU0C=4hX28p4BaSE1XL78BAQ0VcDaLLt8tdUzsg@mail.gmail.com

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2f908e1a3b9c07e43d3ad9ebe6633fae1ed355e3

Modified Files
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doc/src/sgml/ref/refresh_materialized_view.sgml | 10 ++++------
doc/src/sgml/rules.sgml                         |  3 ---
2 files changed, 4 insertions(+), 9 deletions(-)