Remove mirror::String::java_lang_String_.

And simplify ClassLinker::InitWithoutImage().
And finish ObjPtr<>-ification of annotation processing.

Test: m test-art-host-gtest
Test: testrunner.py --host
Bug: 31113334
Change-Id: I882a6c2f2b2a88d6ba34e4759bac4a6caa54cafa
diff --git a/runtime/mirror/class.cc b/runtime/mirror/class.cc
index e6bfe55..cb2708d 100644
--- a/runtime/mirror/class.cc
+++ b/runtime/mirror/class.cc
@@ -1461,12 +1461,12 @@
   // circularity issue during loading the names of its members
   DCHECK(IsIdxLoaded<kVerifyFlags>() || IsRetired<kVerifyFlags>() ||
          IsErroneous<static_cast<VerifyObjectFlags>(kVerifyFlags & ~kVerifyThis)>() ||
-         this == String::GetJavaLangString())
+         this == GetClassRoot<String>())
               << "IsIdxLoaded=" << IsIdxLoaded<kVerifyFlags>()
               << " IsRetired=" << IsRetired<kVerifyFlags>()
               << " IsErroneous=" <<
               IsErroneous<static_cast<VerifyObjectFlags>(kVerifyFlags & ~kVerifyThis)>()
-              << " IsString=" << (this == String::GetJavaLangString())
+              << " IsString=" << (this == GetClassRoot<String>())
               << " status= " << GetStatus<kVerifyFlags>()
               << " descriptor=" << PrettyDescriptor();
 }