Return Object* instead of MaybeObject* from runtime calls.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index af5a2a5bfc82a9a33d2d63ce81f357d6ac63bc2b..2742032b16dd16bbad2fdf3a2a69c72851332d45 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -763,8 +763,6 @@ class ExternalReference BASE_EMBEDDED {
   static ExternalReference store_buffer_overflow_function(
       Isolate* isolate);
   static ExternalReference flush_icache_function(Isolate* isolate);
-  static ExternalReference perform_gc_function(Isolate* isolate);
-  static ExternalReference out_of_memory_function(Isolate* isolate);
   static ExternalReference delete_handle_scope_extensions(Isolate* isolate);
 
   static ExternalReference get_date_field_function(Isolate* isolate);