[SystemZ] Remove getInliningThresholdMultiplier() override

Using this TTI hook is only appropriate for GPU targets that need
to maximally flatten all functions.

The inlining threshold multiplier should not be increased for
ordinary targets -- while this may increase benchmark scores, it
can also result in large code size increases and runaway inlining,
resulting in build OOM/timeouts.

Author: nikic

llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h

@@ -38,7 +38,6 @@ class SystemZTTIImpl : public BasicTTIImplBase<SystemZTTIImpl> {
   /// \name Scalar TTI Implementations
   /// @{
 
-  unsigned getInliningThresholdMultiplier() const { return 3; }
   unsigned adjustInliningThreshold(const CallBase *CB) const;
 
   InstructionCost getIntImmCost(const APInt &Imm, Type *Ty,