RFR: 8198424: Remove G1AllocationContext

[Stefan Johansson]

Hi,

Please review this change to remove G1AllocationContext which no longer 
is needed.

Links
JBS: https://bugs.openjdk.java.net/browse/JDK-8198424
Webrev: http://cr.openjdk.java.net/~sjohanss/8198424/00/

Summary
G1AllocationContext was a very intrusive extension point which made it 
possible to have allocations mapped to a specific context, keeping this 
context over GCs. To support this the allocation-contexts are passed 
around in the G1 code base and it adds a fair bit of complexity. The 
internal code making use of this has been removed and this allow us to 
clean up G1 by removing all use of the G1AllocationContext.

The change is pretty straight forward, the intent is to remove all 
references to G1AllocationContext.

Testing
* Mach5 tier 1-3

Thanks,
Stefan