pgsql: Remove io prefix from pg_stat_io columns

Remove io prefix from pg_stat_io columns

a9c70b46 added the statistics view pg_stat_io which contained columns
"io_context" and "io_object". Given that the columns are in the
pg_stat_io view, the "io" prefix is somewhat redundant, so remove it.

The code variables referring to these fields are kept unchanged so as
they can keep their context about I/O.

Bump catalog version.

Author: Melanie Plageman
Reviewed-by: Kyotaro Horiguchi, Fabrízio de Royes Mello
Discussion: https://postgr.es/m/CAAKRu_aAQoJWrvT2BYYQvJChFKra_O-5ra3jhzKJZqWsTR1CPQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0ecb87e1fa07a733494e35636e55807b0f3fc1ed

Modified Files
--------------
contrib/amcheck/expected/check_heap.out | 4 ++--
contrib/amcheck/sql/check_heap.sql | 4 ++--
doc/src/sgml/monitoring.sgml | 22 ++++++++++-----------
src/backend/catalog/system_views.sql | 4 ++--
src/backend/utils/adt/pgstatfuncs.c | 8 ++++----
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 2 +-
src/test/regress/expected/rules.out | 6 +++---
src/test/regress/expected/stats.out | 34 ++++++++++++++++-----------------
src/test/regress/sql/stats.sql | 34 ++++++++++++++++-----------------
10 files changed, 60 insertions(+), 60 deletions(-)