[vm] Removing debugging break from os_thread_absl.cc

TEST=none, will be cbuild
Bug: b/220994782
Change-Id: Idf1e041b4dfaab16ef6207beecad377aca659738
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/237123
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

runtime/vm/os_thread_absl.cc

@@ -409,7 +409,7 @@ ABSL_NO_THREAD_SAFETY_ANALYSIS
 void Monitor::NotifyAll() {
   // When running with assertions enabled we track the owner.
   ASSERT(IsOwnedByCurrentThread());
-  xdata_.cond()->SignalAll();
+  data_.cond()->SignalAll();
 }
 
 }  // namespace dart