Remove the old type system for proxied resources. These were no longer being used.

ppapi/proxy/ppb_buffer_proxy.cc

Index: ppapi/proxy/ppb_buffer_proxy.cc
diff --git a/ppapi/proxy/ppb_buffer_proxy.cc b/ppapi/proxy/ppb_buffer_proxy.cc
index 57dba6ca6f3ffbcad6ef9ee6f1f7a6c76ae1bffe..f25d7e2bcb34f28515039f9dad7b00f0b15df0c3 100644
--- a/ppapi/proxy/ppb_buffer_proxy.cc
+++ b/ppapi/proxy/ppb_buffer_proxy.cc
@@ -45,10 +45,6 @@ Buffer::~Buffer() {
   Unmap();
 }
 
-Buffer* Buffer::AsBuffer() {
-  return this;
-}
-
 ppapi::thunk::PPB_Buffer_API* Buffer::AsPPB_Buffer_API() {
   return this;
 }