Dont send a HTTP POST when removing non-persisted nested fields

Hey I was creating a extension and noticed that if you remove a non-persisted nested field it sends a POST to the server trying to remove it.

A core example of this is in Option Values:

When you click the "Add Option Value" link
And you click the newly created "Remove" icon
Then the server sends a HTTP POST request that fails with 404 or 302

I did the patch against 1-3-stable as that's what I'm using currently, but I can change it to use master if you like.

I'm writing up a test for it now.