* lisp/character-fold.el: Remove special case-folding support
(character-fold-to-regexp): Remove special code for case-folding. Char-fold search still respects the `case-fold-search' variable (i.e., f matches F). This only removes the code that was added to ensure that f also matched all chars that F matched. For instance, after this commit, f no longer matches 𝔽. This was necessary because the logic created a regexp with 2^(length of the string) redundant paths. So, when a very long string "almost" matched, Emacs took a very long time to figure out that it didn't. This became particularly relevant because isearch's lazy-highlight does a search bounded by (1- match-end) (which, in most circumstances, is a search that almost matches). A recipe for this can be found in bug#22090.
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