pgsql: Simplify description of --data-checksums in documentation ofini

Simplify description of --data-checksums in documentation of initdb

The documentation mentioned that data checksums cannot be changed after
initialization, which is not true as pg_checksums can do that with its
--enable option introduced in v12.  This simply removes the sentence
telling so.

Reported-by: Basil Bourque
Author: Michael Paquier
Reviewed-by: Daniel Gustafsson
Discussion: https://postgr.es/m/15909-e9d74271f1647472@postgresql.org
Backpatch-through: 12

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1c1602b8b685a68796f8ba48e41f778c0c42ba43

Modified Files
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doc/src/sgml/ref/initdb.sgml | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)