Revert of MIPS: Fix bad RegisterConfiguration usage in InstructionSequence unit tests.

src/compiler/instruction.cc

Index: src/compiler/instruction.cc
diff --git a/src/compiler/instruction.cc b/src/compiler/instruction.cc
index 44d525e2c5d4de6a99de33b022be2f6c307f5ba2..174ee300fee63348fbf0791801528d628da2b2a2 100644
--- a/src/compiler/instruction.cc
+++ b/src/compiler/instruction.cc
@@ -12,8 +12,7 @@
 namespace internal {
 namespace compiler {
 
-const RegisterConfiguration* (*GetRegConfig)() =
-    RegisterConfiguration::Turbofan;
+const auto GetRegConfig = RegisterConfiguration::Turbofan;
 
 FlagsCondition CommuteFlagsCondition(FlagsCondition condition) {
   switch (condition) {
@@ -982,11 +981,6 @@
   PrintBlock(GetRegConfig(), block_id);
 }
 
-const RegisterConfiguration*
-InstructionSequence::GetRegisterConfigurationForTesting() {
-  return GetRegConfig();
-}
-
 FrameStateDescriptor::FrameStateDescriptor(
     Zone* zone, FrameStateType type, BailoutId bailout_id,
     OutputFrameStateCombine state_combine, size_t parameters_count,