Bug 1322080 (part 2) - Remove XPC_MAP_WANT_POST_CREATE_PROTOTYPE. r=peterv.

It's never defined, and there's a comment in
XPCWrappedNativeProto::CallPostCreatePrototype() explaining how
PostCreatePrototype() doesn't have an associated "want" check.

js/xpconnect/public/xpc_map_end.h

@@ -127,10 +127,8 @@ NS_IMETHODIMP XPC_MAP_CLASSNAME::HasInstance(nsIXPConnectWrappedNative* wrapper,
     {NS_ERROR("never called"); return NS_ERROR_NOT_IMPLEMENTED;}
 #endif
 
-#ifndef XPC_MAP_WANT_POST_CREATE_PROTOTYPE
 NS_IMETHODIMP XPC_MAP_CLASSNAME::PostCreatePrototype(JSContext* cx, JSObject* proto)
     {return NS_OK;}
-#endif
 
 /**************************************************************/
 
@@ -181,10 +179,6 @@ NS_IMETHODIMP XPC_MAP_CLASSNAME::PostCreatePrototype(JSContext* cx, JSObject* pr
 #undef XPC_MAP_WANT_HASINSTANCE
 #endif
 
-#ifdef XPC_MAP_WANT_POST_CREATE_PROTOTYPE
-#undef XPC_MAP_WANT_POST_CREATE_PROTOTYPE
-#endif
-
 #ifdef XPC_MAP_FLAGS
 #undef XPC_MAP_FLAGS
 #endif