Make error code prefix of general exception an empty string

* This is done to avoid a breaking change in the api since this would
  change the error code of already existing exceptions

Signed-off-by: Yannic Klem <Yannic.Klem@bosch.io>

base/model/src/main/java/org/eclipse/ditto/base/model/exceptions/GeneralException.java

@@ -22,6 +22,6 @@ public interface GeneralException {
     /**
      * Error code prefix of errors emitted by any Ditto service.
      */
-    String ERROR_CODE_PREFIX = "general" + ":";
+    String ERROR_CODE_PREFIX = "";
 
 }