RDS DB Cluster remove MasterUserPassword from exclusion with MasterUsername (#3106)

Author: kddejong

src/cfnlint/data/AdditionalSpecs/Exclusive.json

@@ -100,8 +100,7 @@
   },
   "AWS::RDS::DBCluster": {
    "SnapshotIdentifier": [
-    "MasterUsername",
-    "MasterUserPassword"
+    "MasterUsername"
    ]
   },
   "AWS::RDS::DBInstance": {