Refactor Forecast to also use shared AWSError class

moto/forecast/exceptions.py

@@ -1,22 +1,6 @@
 from __future__ import unicode_literals
 
-import json
-
-
-class AWSError(Exception):
-    TYPE = None
-    STATUS = 400
-
-    def __init__(self, message, type=None, status=None):
-        self.message = message
-        self.type = type if type is not None else self.TYPE
-        self.status = status if status is not None else self.STATUS
-
-    def response(self):
-        return (
-            json.dumps({"__type": self.type, "message": self.message}),
-            dict(status=self.status),
-        )
+from moto.core.exceptions import AWSError
 
 
 class InvalidInputException(AWSError):