Remove mirror::Reference::java_lang_ref_Reference.

And some #include cleanup after previous CLs removing
static GcRoot<>s.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 31113334
Change-Id: I56b34637f9d793ed7680696a1eeedd07d061ad00
diff --git a/runtime/class_table-inl.h b/runtime/class_table-inl.h
index 5da5470..6b6fe34 100644
--- a/runtime/class_table-inl.h
+++ b/runtime/class_table-inl.h
@@ -20,6 +20,7 @@
 #include "class_table.h"
 
 #include "gc_root-inl.h"
+#include "mirror/class.h"
 #include "oat_file.h"
 
 namespace art {