Remove scratch register requirement from LoadInstanceDescriptors on arm and mips.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index dacfc0ed5c8a74b6bc40142f2b48cf10374b0f8e..052387ab0156f5587089cd6e288b93d59cf62209 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -5302,8 +5302,7 @@ void MacroAssembler::EnsureNotWhite(
 
 
 void MacroAssembler::LoadInstanceDescriptors(Register map,
-                                             Register descriptors,
-                                             Register scratch) {
+                                             Register descriptors) {
   lw(descriptors, FieldMemOperand(map, Map::kDescriptorsOffset));
 }