docs(lambda): remove references to deprecated addVersion() (aws#19601)

fixes aws#19594 

----

### All Submissions:

* [x] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/master/INTEGRATION_TESTS.md)?
	* [ ] Did you use `cdk-integ` to deploy the infrastructure and generate the snapshot (i.e. `cdk-integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-applicationautoscaling/README.md

@@ -222,7 +222,7 @@ const handler = new lambda.Function(this, 'MyFunction', {
   reservedConcurrentExecutions: 2,
 });
 
-const fnVer = handler.addVersion('CDKLambdaVersion', undefined, 'demo alias', 10);
+const fnVer = handler.currentVersion;
 
 const target = new appscaling.ScalableTarget(this, 'ScalableTarget', {
   serviceNamespace: appscaling.ServiceNamespace.LAMBDA,

packages/@aws-cdk/aws-codedeploy/README.md

@@ -207,7 +207,7 @@ To create a new CodeDeploy Deployment Group that deploys to a Lambda function:
 ```ts
 declare const myApplication: codedeploy.LambdaApplication;
 declare const func: lambda.Function;
-const version = func.addVersion('1');
+const version = func.currentVersion;
 const version1Alias = new lambda.Alias(this, 'alias', {
   aliasName: 'prod',
   version,
@@ -222,7 +222,7 @@ const deploymentGroup = new codedeploy.LambdaDeploymentGroup(this, 'BlueGreenDep
 
 In order to deploy a new version of this function:
 
-1. Increment the version, e.g. `const version = func.addVersion('2')`.
+1. Reference the version with the latest changes `const version = func.currentVersion`.
 2. Re-deploy the stack (this will trigger a deployment).
 3. Monitor the CodeDeploy deployment as traffic shifts between the versions.
 

packages/@aws-cdk/aws-codepipeline-actions/README.md

@@ -765,7 +765,7 @@ const func = new lambda.Function(this, 'Lambda', {
   runtime: lambda.Runtime.NODEJS_12_X,
 });
 // used to make sure each CDK synthesis produces a different Version
-const version = func.addVersion('NewVersion');
+const version = func.currentVersion;
 const alias = new lambda.Alias(this, 'LambdaAlias', {
   aliasName: 'Prod',
   version,

packages/@aws-cdk/aws-lambda/lib/alias.ts

@@ -75,7 +75,7 @@ export interface AliasProps extends AliasOptions {
   /**
    * Function version this alias refers to
    *
-   * Use lambda.addVersion() to obtain a new lambda version to refer to.
+   * Use lambda.currentVersion to reference a version with your latest changes.
    */
   readonly version: IVersion;
 }