doc: Remove buggy ICU collation from documentation

doc: Remove buggy ICU collation from documentation

We have had multiple reports that point to the
'@colReorder=latn-digit' collation customization being buggy.  We have
reported this to ICU and are waiting for a fix.  In the meantime,
remove references to this from the documentation and replace it by
another reordering example.  Apparently, many users have been picking
up this example specifically from the documentation.

Author: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
Discussion: https://www.postgresql.org/message-id/flat/153201618542.1404.3611626898935613264%40wrigleys.postgresql.org