ART: Refactor class-linker methods

Hide the LookupClass with hash version. Clients should not have to
know about that performance detail.

Hide FindClassInPathClassLoader. This is an implementation detail.

Test: m test-art-host
Change-Id: I2378c6fed8d7d1fb1ead8e042b4cf07228adf25c
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 439849b..f29ed1f 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -2237,8 +2237,7 @@
     }
     CHECK(h_class->IsRetired());
     // Get the updated class from class table.
-    klass = LookupClass(self, descriptor, ComputeModifiedUtf8Hash(descriptor),
-                        h_class.Get()->GetClassLoader());
+    klass = LookupClass(self, descriptor, h_class.Get()->GetClassLoader());
   }
 
   // Wait for the class if it has not already been linked.