Revert of GC plugin: improve error reporting when tracing illegal fields.

tools/clang/blink_gc_plugin/tests/fields_illegal_tracing.txt

Index: tools/clang/blink_gc_plugin/tests/fields_illegal_tracing.txt
diff --git a/tools/clang/blink_gc_plugin/tests/fields_illegal_tracing.txt b/tools/clang/blink_gc_plugin/tests/fields_illegal_tracing.txt
deleted file mode 100644
index 5e428dcd44671781eaf1cde02021c99c3169e037..0000000000000000000000000000000000000000
--- a/tools/clang/blink_gc_plugin/tests/fields_illegal_tracing.txt
+++ /dev/null
@@ -1,50 +0,0 @@
-In file included from fields_illegal_tracing.cpp:5:
-./fields_illegal_tracing.h:32:1: warning: [blink-gc] Class 'PartObject' contains invalid fields.
-class PartObject {
-^
-./fields_illegal_tracing.h:37:5: note: [blink-gc] OwnPtr field 'm_obj1' to a GC managed class declared here:
-    OwnPtr<HeapObject> m_obj1;
-    ^
-./fields_illegal_tracing.h:38:5: note: [blink-gc] RefPtr field 'm_obj2' to a GC managed class declared here:
-    RefPtr<HeapObject> m_obj2;
-    ^
-./fields_illegal_tracing.h:40:5: note: [blink-gc] std::unique_ptr field 'm_obj4' to a GC managed class declared here:
-    std::unique_ptr<HeapObject> m_obj4;
-    ^
-./fields_illegal_tracing.h:43:1: warning: [blink-gc] Class 'HeapObject' contains invalid fields.
-class HeapObject : public GarbageCollectedFinalized<HeapObject> {
-^
-./fields_illegal_tracing.h:48:5: note: [blink-gc] OwnPtr field 'm_obj1' to a GC managed class declared here:
-    OwnPtr<HeapObject> m_obj1;
-    ^
-./fields_illegal_tracing.h:49:5: note: [blink-gc] RefPtr field 'm_obj2' to a GC managed class declared here:
-    RefPtr<HeapObject> m_obj2;
-    ^
-./fields_illegal_tracing.h:51:5: note: [blink-gc] std::unique_ptr field 'm_obj4' to a GC managed class declared here:
-    std::unique_ptr<HeapObject> m_obj4;
-    ^
-fields_illegal_tracing.cpp:9:1: warning: [blink-gc] Class 'PartObject' has untraced or not traceable fields.
-void PartObject::trace(Visitor* visitor) {
-^
-./fields_illegal_tracing.h:37:5: note: [blink-gc] Untraceable field 'm_obj1' declared here:
-    OwnPtr<HeapObject> m_obj1;
-    ^
-./fields_illegal_tracing.h:38:5: note: [blink-gc] Untraceable field 'm_obj2' declared here:
-    RefPtr<HeapObject> m_obj2;
-    ^
-./fields_illegal_tracing.h:40:5: note: [blink-gc] Untraceable field 'm_obj4' declared here:
-    std::unique_ptr<HeapObject> m_obj4;
-    ^
-fields_illegal_tracing.cpp:16:1: warning: [blink-gc] Class 'HeapObject' has untraced or not traceable fields.
-void HeapObject::trace(Visitor* visitor) {
-^
-./fields_illegal_tracing.h:48:5: note: [blink-gc] Untraceable field 'm_obj1' declared here:
-    OwnPtr<HeapObject> m_obj1;
-    ^
-./fields_illegal_tracing.h:49:5: note: [blink-gc] Untraceable field 'm_obj2' declared here:
-    RefPtr<HeapObject> m_obj2;
-    ^
-./fields_illegal_tracing.h:51:5: note: [blink-gc] Untraceable field 'm_obj4' declared here:
-    std::unique_ptr<HeapObject> m_obj4;
-    ^
-4 warnings generated.