RFR: 8273482: Remove "foreground work" concept from WorkGang [v2]

[Per Liden]

On Fri, 10 Sep 2021 07:52:32 GMT, Ralf Schmelter <rschmelter at openjdk.org> wrote:

> The reason I've added this was, that for the shenandoah GC the heap iteration would run into assertions if not called from the VM thread. Maybe this has changed in the meantime.

As mentioned in my previous comment. This PR removes those asserts since they were overly strict.

-------------

PR: https://git.openjdk.java.net/jdk/pull/5410