module: unicode: remove unused tolower transformations

With the previous patch this yields

$ size -G ./module/zfs.ko ./module/zfs.new.ko
      text       data        bss      total filename
   2865126    1597982     755768    5218876 ./module/zfs.ko
   2864038    1429784     755768    5049590 ./module/zfs.new.ko
     -1088    -168198
       -1k      -164k

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #16704