pgsql: doc: Update ALTER COLLATION wording

doc: Update ALTER COLLATION wording

The original text on refreshing collation versions was written
specifically for ICU, and then information for other providers was
incrementally tacked on at the end. Reword this to be a bit more
general and less reflective of how it was added.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9a50f2e51cf89889a08922b74dbe68486f20b760

Modified Files
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doc/src/sgml/ref/alter_collation.sgml | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)