Readme for Autopilot modules reference unused "enable_autopilot" input

[grsiepka]

In the Readme examples for both the beta-autopilot-private-cluster and beta-autopilot-public-cluster, there's reference to an input: enable_autopilot = true, however that doesn't seem to be a valid input (maybe at one time it was?) and its not listed in the list of inputs in the module documentation.

https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/blob/master/modules/beta-autopilot-private-cluster/README.md#usage

https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/blob/master/modules/beta-autopilot-public-cluster/README.md#usage