initdb: Refactor PG_CMD_PUTS loops

Keeping the SQL commands that initdb runs in string arrays before
feeding them to PG_CMD_PUTS() seems unnecessarily verbose and
inflexible.  In some cases, the array only has one member.  In other
cases, one might want to use PG_CMD_PRINTF() instead, to parametrize a
command, but that would require breaking up the loop or using
workarounds like replace_token().  Unwind all that; it's much simpler
that way.

Reviewed-by: John Naylor <john.naylor@enterprisedb.com>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://www.postgresql.org/message-id/flat/2c50823b-f453-bb97-e38b-34751c51dcdf%40enterprisedb.com

Author: petere