Fix event reporting from the debugger thread

The debugger thread may trigger events (like CLASS PREPARE after the
initalization of a class while processing a command).

This CL removes the incorrect CHECK that makes the runtime abort in
this case. However, we do check that only the debugger thread can
report an event while it is already processing a command.

Bug: 33032664
Test: art/tools/run-jdwp-tests.sh '--mode=host' '--variant=X64'

(cherry picked from commit af8bcf83)

Change-Id: Id2e4362393203935e820586560800b300c6dd3a3