pgsql: Fix some typos, grammar and style in docs and comments

Fix some typos, grammar and style in docs and comments

The portions fixing the documentation are backpatched where needed.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20210210235557.GQ20012@...
backpatch-through: 9.6

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a8f26f6c8882170d1fa7b86f2d83a314ee746e7e

Modified Files
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doc/src/sgml/charset.sgml         | 2 +-
doc/src/sgml/pageinspect.sgml     | 2 +-
doc/src/sgml/protocol.sgml        | 4 ++--
doc/src/sgml/ref/create_type.sgml | 2 +-
doc/src/sgml/ref/drop_index.sgml  | 2 +-
doc/src/sgml/rules.sgml           | 2 +-
6 files changed, 7 insertions(+), 7 deletions(-)