fix(realtimebidding): update the API

#### realtimebidding:v1alpha

The following keys were changed:
- schemas.BiddingFunction.properties.biddingFunction.description

discovery/realtimebidding-v1alpha.json

@@ -178,15 +178,15 @@
       }
     }
   },
-  "revision": "20210308",
+  "revision": "20210406",
   "rootUrl": "https://realtimebidding.googleapis.com/",
   "schemas": {
     "BiddingFunction": {
       "description": "The bidding function to be executed as part of the TURTLEDOVE simulation experiment bidding flow.",
       "id": "BiddingFunction",
       "properties": {
         "biddingFunction": {
-          "description": "The raw Javascript source code of the bidding function. The function takes in a Javascript object, `inputs`, that contains the following named fields: `openrtbContextualBidRequest` OR `googleContextualBidRequest`, `customContextualSignal`, `interestBasedBidData`, `interestGroupData`, `recentImpressionAges`, and returns the bid price CPM (double). Example: ``` /* Returns a bid price CPM (double). * * @param {Object} inputs an object with the * following named fields: * - openrtbContextualBidRequest * OR googleContextualBidRequest * - customContextualSignal * - interestBasedBidData * - interestGroupData * - recentImpressionAges */ function biddingFunction(inputs) { ... return inputs.interestBasedBidData.cpm * inputs.customContextualSignals.placementMultiplier; } ```",
+          "description": "The raw Javascript source code of the bidding function.",
           "type": "string"
         },
         "name": {

src/apis/realtimebidding/v1alpha.ts

@@ -130,7 +130,7 @@ export namespace realtimebidding_v1alpha {
    */
   export interface Schema$BiddingFunction {
     /**
-     * The raw Javascript source code of the bidding function. The function takes in a Javascript object, `inputs`, that contains the following named fields: `openrtbContextualBidRequest` OR `googleContextualBidRequest`, `customContextualSignal`, `interestBasedBidData`, `interestGroupData`, `recentImpressionAges`, and returns the bid price CPM (double). Example: ``` /x Returns a bid price CPM (double). * * @param {Object\} inputs an object with the * following named fields: * - openrtbContextualBidRequest * OR googleContextualBidRequest * - customContextualSignal * - interestBasedBidData * - interestGroupData * - recentImpressionAges x/ function biddingFunction(inputs) { ... return inputs.interestBasedBidData.cpm * inputs.customContextualSignals.placementMultiplier; \} ```
+     * The raw Javascript source code of the bidding function.
      */
     biddingFunction?: string | null;
     /**