patch 9.1.0297: Patch 9.1.0296 causes too many issues

Problem:  Patch 9.1.0296 causes too many issues
          (Tony Mechelynck, @chdiza, CI)
Solution: Back out the change for now

Revert "patch 9.1.0296: regexp: engines do not handle case-folding well"

This reverts commit 7a27c108e0509f3255ebdcb6558e896c223e4d23 it causes
issues with syntax highlighting and breaks the FreeBSD and MacOS CI. It
needs more work.

fixes: #14487

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 451720a..5e4fadd 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -5666,12 +5666,7 @@
     for (;;)
     {
 	match = TRUE;
-	// skip regstart
-	len2 = MB_CHAR2LEN(regstart);
-	if (enc_utf8 && len2 > 1 && MB_CHAR2LEN(PTR2CHAR(rex.line + col)) != len2)
-	    // because of case-folding of the previously matched text, we may need
-	    // to skip fewer bytes than mb_char2len(regstart)
-	    len2 = mb_char2len(utf_fold(regstart));
+	len2 = MB_CHAR2LEN(regstart); // skip regstart
 	for (len1 = 0; match_text[len1] != NUL; len1 += MB_CHAR2LEN(c1))
 	{
 	    c1 = PTR2CHAR(match_text + len1);
@@ -7508,7 +7503,7 @@
 
 	// If match_text is set it contains the full text that must match.
 	// Nothing else to try. Doesn't handle combining chars well.
-	if (prog->match_text != NULL && *prog->match_text != NUL && !rex.reg_icombine)
+	if (prog->match_text != NULL && !rex.reg_icombine)
 	{
 	    retval = find_match_text(&col, prog->regstart, prog->match_text);
 	    if (REG_MULTI)