[Outliner] Remove no red zone requirment for AArch64

AArch64 doesn't require -mno-red-zone; stack fixups are sufficient here. This was
unnecessarily copied over from the X86 target.

(You can now outline with red zones! Yay!)

Removing the requirement passes all Single/MultiSource tests.

llvm-svn: 298734

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

@@ -4280,7 +4280,7 @@ unsigned AArch64InstrInfo::getOutliningBenefit(size_t SequenceSize,
 }
 
 bool AArch64InstrInfo::isFunctionSafeToOutlineFrom(MachineFunction &MF) const {
-  return MF.getFunction()->hasFnAttribute(Attribute::NoRedZone);
+  return true;
 }
 
 AArch64GenInstrInfo::MachineOutlinerInstrType