[3.11] Fix grammatical error in stringprep documentation (GH-108414) (#108538)

Fix grammatical error in stringprep documentation (GH-108414)

Remove the word "them", which didn't make grammatical sense.

(cherry picked from commit cd0a8aece974330ef44ffe4e0f2e8aa632e98438)

Co-authored-by: Matthew James Kraai <kraai@ftbfs.org>
Co-authored-by: KRAAI, MATTHEW [VISUS] <mkraai@its.jnj.com>