patch 9.1.0624: ex command modifiers not found

patch 9.1.0624: ex command modifiers not found

Problem:  ex command modifiers are not found
          (Ingo Karkat, after v9.1.0352)
Solution: partly revert patch v9.1.0352, ignore :{ and :}
          when expanding ex commands

The issue is, that the :keepmarks command can be abbreviated to :kee or
:keep or :keepm but not to e.g. :ke (because that would be the :exe
command :k with register e).

This basically means, we need `:kee` sorted before `:keepalt` but at the
same time `:keepmarks` sorted after the `:keepalt` command in the
cmdmod_info_tab table. Due to this, the binary search may not work
correctly, so let's revert that part of patch v9.1.0352.

fixes: #15305
closes: #15336

Signed-off-by: Christian Brabandt <cb@256bit.org>