Revert "Fixed double decode subject"

This reverts commit e3b9d9e599.

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -995,10 +995,9 @@ public class MessageHelper {
         if (subject == null)
             return null;
 
-        // https://github.com/eclipse-ee4j/mail/issues/423
-
         subject = subject.replaceAll("\\?=\\r?\\n\\s+=\\?", "\\?==\\?");
         subject = MimeUtility.unfold(subject);
+        subject = new String(subject.getBytes(StandardCharsets.ISO_8859_1));
         subject = decodeMime(subject);
 
         return subject;