Update queryCompatibleTest to not require serializing an empty body (#2681)

Author: Madrigal

smithy-aws-protocol-tests/model/rpcv2Cbor/query-compatible.smithy

@@ -17,8 +17,7 @@ use smithy.test#httpResponseTests
         headers: { "smithy-protocol": "rpc-v2-cbor", Accept: "application/cbor" }
         forbidHeaders: ["x-amzn-query-mode"]
         uri: "/service/NonQueryCompatibleRpcV2Protocol/operation/QueryIncompatibleOperation"
-        body: "{}"
-        bodyMediaType: "application/json"
+        body: ""
     }
 ])
 @idempotent