minikube delete doesn't remove subnodes machine directory

[daehyeok]

❯ ls
server-key.pem server.pem
❯ minikube start -p test-profile -n 2
😄  [test-profile] minikube v1.15.1 on Darwin 10.15.7
✨  Automatically selected the docker driver
👍  Starting control plane node test-profile in cluster test-profile
🔥  Creating docker container (CPUs=2, Memory=1988MB) ...
🐳  Preparing Kubernetes v1.20.0 on Docker 20.10.0 ...
🔗  Configuring CNI (Container Networking Interface) ...
🔎  Verifying Kubernetes components...
🌟  Enabled addons: storage-provisioner, default-storageclass

❗  Multi-node clusters are currently experimental and might exhibit unintended behavior.
📘  To track progress on multi-node clusters, see https://github.com/kubernetes/minikube/issues/7538.

👍  Starting node test-profile-m02 in cluster test-profile
🔥  Creating docker container (CPUs=2, Memory=1988MB) ...
🌐  Found network options:
    ▪ NO_PROXY=192.168.49.2
🐳  Preparing Kubernetes v1.20.0 on Docker 20.10.0 ...
    ▪ env NO_PROXY=192.168.49.2
🔎  Verifying Kubernetes components...
🏄  Done! kubectl is now configured to use "test-profile" cluster and "default" namespace by default
❯ ls
server-key.pem   server.pem       test-profile     test-profile-m02
❯ minikube delete -p test-profile
🔥  Deleting "test-profile" in docker ...
🔥  Deleting container "test-profile" ...
🔥  Deleting container "test-profile-m02" ...
🔥  Removing /Users/daehyeok/.minikube/machines/test-profile ...
💀  Removed all traces of the "test-profile" cluster.
❯ ls
server-key.pem   server.pem       test-profile-m02
~/.minikube/machines ❯

[priyawadhwa]

@daehyeok thank you for catching this and opening a PR to fix it!