RFR: 8221219: ZGC: Remove ZStallOnOutOfMemory option

[Per Liden]

I should perhaps clarify that this option is enabled by default, and 
it's disabling it that is not so useful.

/Per

On 3/21/19 9:12 AM, Per Liden wrote:
> The ZStallOnOutOfMemory option was added in ZGC's early days, and was at 
> that time useful when testing and debugging. These days it's not so 
> useful, and I can't really see anyone wanting to use it when running a 
> real application as is can/will cause pre-mature OOMEs to be thrown. I 
> suggest we remove it.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8221219
> Webrev: http://cr.openjdk.java.net/~pliden/8221219/webrev.0
> 
> (Change builds on JDK-8221212, which is out for review)
> 
> /Per