pgsql: Fix erroneous documentation about noise word GROUP.

Fix erroneous documentation about noise word GROUP.

GRANT, REVOKE, and some allied commands allow the noise word GROUP
before a role name (cf. grantee production in gram.y). This option
does not exist elsewhere, but it had nonetheless snuck into the
documentation for ALTER ROLE, ALTER USER, and CREATE SCHEMA.

Seems to be a copy-and-pasteo in commit 31eae6028, which did expand the
syntax choices here, but not in that way. Back-patch to 9.5 where that
came in.

Discussion: https://postgr.es/m/20170916123750.8885.66941@wrigleys.postgresql.org

Branch
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REL9_5_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6f5e7a87406f2a52c270b34f257f1c41d631b575

Modified Files
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doc/src/sgml/ref/alter_role.sgml | 2 +-
doc/src/sgml/ref/alter_user.sgml | 2 +-
doc/src/sgml/ref/create_schema.sgml | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)