Cannot update action kind if runtime is no longer supported

I tried to update the `kind` of an action that has an old runtime that has been removed, but this fails with the following error message:

```
$ wsk action update foo --kind nodejs:10
error: Unable to create action 'foo': The 'nodejs:10-fat' runtime is no longer supported. You may read and delete but not update or invoke this action. (code Jhgg2GzINamHp5yxACGBXjCbcViyU8bD)
```

The `nodejs:10-fat` is indeed an old runtime that has been removed. I found the error message at:

https://github.com/apache/incubator-openwhisk/blob/master/common/scala/src/main/scala/org/apache/openwhisk/http/ErrorResponse.scala#L56-L63

so it looks like a backend issue and not an issue from the `wsk` CLI.

I'd have expected that it is possible to update the `kind` in order to update all actions that use some deprecated runtime without having to redeploy the code.

cc: @csantanapr as discussed on Slack