Remove the workaround for ForkJoin to spin up threads

[Sanne]

Describe the bug
We set -J-Djava.util.concurrent.ForkJoinPool.common.parallelism=1 in NativeImageBuildStep
to workaround for

• Use of default ForkJoinPool during static init is unreliable oracle/graal#660

It seems the GraalVM issue was resolved; are we safe to remove the workaround from Quarkus?

@stuartwdouglas needs your opinion at least

[gsmet]

I'm not sure the commit has been included in 19.2.x:
oracle/graal@e78fc21

From what I can see, it's only in 19.3 but I might be wrong.

[gwenneg]

This was included in 19.3.0 indeed.

[stuartwdouglas]

This would be a good fix to have, I think it may speed up our native builds as I know the native compilation does use fork join internally in places.

[machi1990]

This was included in 19.3.0 indeed.

@gwenneg Good to know. Any chance you could take this as part of your on going work with 19.3.0 ?

[gwenneg]

@machi1990 Sure, this could be part of #5358

[machi1990]

Thanks @gwenneg

[gwenneg]

Done in #5358.