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_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a7359913a1c22e8c04f37140b9d983919baf10b2

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(-)