git: openjdk/loom: fibers: Remove StepRequest::is_vthread field. It's not needed anymore

[duke]

Changeset: b839dcf3
Author:    Chris Plummer <chris.plummer at oracle.com>
Date:      2021-09-16 20:03:09 +0000
URL:       https://git.openjdk.java.net/loom/commit/b839dcf399884154dd61e4917e15846309c5c809

Remove StepRequest::is_vthread field. It's not needed anymore

! src/jdk.jdwp.agent/share/native/libjdwp/stepControl.c
! src/jdk.jdwp.agent/share/native/libjdwp/stepControl.h