Fix: TestMutateRow_Generic_Headers (#1540)

Mutate rows is grabbing the `appProfileId` from the client. 

https://togithub.com/googleapis/nodejs-bigtable/blob/eb2cd9fb5134e454709b724d99b4da2db9ccadc0/src/tabular-api-surface.ts#L765

We should modify the test proxy test here to do the same.

Author: kevkim-codes

testproxy/known_failures.txt

@@ -1,4 +1,3 @@
-TestMutateRow_Generic_Headers\|
 TestMutateRow_Generic_DeadlineExceeded\|
 TestMutateRows_Generic_CloseClient\|
 TestMutateRows_Retry_WithRoutingCookie\|

testproxy/services/mutate-row.js

@@ -23,10 +23,11 @@ const mutateRow = ({clientMap}) =>
   normalizeCallback(async rawRequest => {
     const {request} = rawRequest;
     const {request: mutateRequest} = request;
-    const {appProfileId, mutations, tableName, rowKey} = mutateRequest;
-
+    const {mutations, tableName, rowKey} = mutateRequest;
     const {clientId} = request;
+    const appProfileId = clientMap.get(clientId).appProfileId;
     const client = clientMap.get(clientId)[v2];
+
     await client.mutateRow({
       appProfileId,
       mutations,