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_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/514f0ae4f40f322b1a10bd774abd4b4d01c97a99

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(-)