[debugger] remove debugger statement support from FCG/CS.

src/compiler/ast-graph-builder.cc

Index: src/compiler/ast-graph-builder.cc
diff --git a/src/compiler/ast-graph-builder.cc b/src/compiler/ast-graph-builder.cc
index 4023d1d3528e7cb41c144beb575aa6e06b355f74..5c8056f73d5135bb3a8f7ccd4fc43752cf07142e 100644
--- a/src/compiler/ast-graph-builder.cc
+++ b/src/compiler/ast-graph-builder.cc
@@ -1285,10 +1285,8 @@ void AstGraphBuilder::VisitTryFinallyStatement(TryFinallyStatement* stmt) {
 
 
 void AstGraphBuilder::VisitDebuggerStatement(DebuggerStatement* stmt) {
-  Node* node =
-      NewNode(javascript()->CallRuntime(Runtime::kHandleDebuggerStatement));
-  PrepareFrameState(node, stmt->DebugBreakId());
-  environment()->MarkAllLocalsLive();
+  // Debugger statement is supported only by going through Ignition first.
+  UNREACHABLE();
 }