remove special processing for U+03B9/U+03BC/U+A64B

* enc/unicode.c: Remove special processing for U+03B9/U+03BC/U+A64B
  (GREEK SMALL LETTERs IOTA/MU, CYRILLIC SMALL LETTER MONOGRAPH UK)
  from onigenc_unicode_case_map and simplify code.

* enc/unicode/case-folding.rb: Remove check for U+03B9/U+03BC/U+A64B.

This and the previous few related commits make sure that we won't hit
the equivalent of bug #12990 anymore for future updates of Unicode versions.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56976 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

enc/unicode.c

@@ -768,19 +768,10 @@ onigenc_unicode_case_map(OnigCaseFoldType* flagP,
 		    }
 		}
 	    }
-	    else if ((folded = onigenc_unicode_unfold1_lookup(code)) != 0) {  /* data about character found in CaseUnfold_11_Table */
-		if (flags&OnigCaseFoldFlags(folded->n)) { /* needs and data availability match */
-		    MODIFIED;
-		    if (flags&OnigCaseFoldFlags(folded->n)&ONIGENC_CASE_TITLECASE)
-		        code = folded->code[1];
-		    else
-			code = folded->code[0];
-		}
-		else if ((flags&(ONIGENC_CASE_UPCASE))
-			 && (code==0x03B9||code==0x03BC||code==0xA64B)) { /* GREEK SMALL LETTERs IOTA/MU, */
-		    MODIFIED;                                             /* CYRILLIC SMALL LETTER MONOGRAPH UK */
-		    code = folded->code[1];
-		}
+	    else if ((folded = onigenc_unicode_unfold1_lookup(code)) != 0  /* data about character found in CaseUnfold_11_Table */
+		     && flags&OnigCaseFoldFlags(folded->n)) { /* needs and data availability match */
+		MODIFIED;
+		code = folded->code[(flags&OnigCaseFoldFlags(folded->n)&ONIGENC_CASE_TITLECASE) ? 1 : 0];
 	    }
 	}
 	to += ONIGENC_CODE_TO_MBC(enc, code, to);

enc/unicode/case-folding.rb

@@ -305,11 +305,7 @@ class CaseMapping
         when item.upper  then  flags += '|U'
         when item.lower  then  flags += '|D'
         else
-          unless from=='03B9' or from=='03BC' or from=='A64B'
-            # cf. code==0x03B9||code==0x03BC||code==0xA64B in enc/unicode.c,
-            # towards the end of function onigenc_unicode_case_map
-            raise "Unpredicted case 0 in enc/unicode/case_folding.rb. Please contact https://bugs.ruby-lang.org/."
-          end
+          raise "Unpredicted case 0 in enc/unicode/case_folding.rb. Please contact https://bugs.ruby-lang.org/."
         end
         unless item.upper == item.title
           if item.code == item.title