fix AutoPairsFastWrap: remove wrong `\` inside `[]`

[tomtomjhj]

'\v[\{\[\(\<]' matches '\' because the collection pattern (:help /[]) matches any single char in the collection even though \v is used. Because of this, AutoPairsFastWrap() on texts like {\bar{|}\asdf} didn't work.

This patch removes such wrong \s.