RFR: Avoid stub when calling to write-barrier from C2, remove all related code

[Aleksey Shipilev]

On 11/19/18 7:13 PM, Roman Kennke wrote:
> http://cr.openjdk.java.net/~rkennke/remove-c2-wb-stub/webrev.01/

That must be webrev.02. Looks good.

-Aleksey