runtime(doc): Revert outdated comment in completeopt's fuzzy documentation

runtime(doc): Revert outdated comment in completeopt's fuzzy documentation

Originally, `:set completeopt+=fuzzy` did not affect how the candidate
list is collected in default keyword completion. A comment was added to
documentation as part of #14912 to clarify it. #15193 later changed the
fuzzy behavior to now change the candidate collection behavior as well
so the clarification in docs is now wrong. Remove them here.

closes: #15656

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>