[NFC][DebugInfo] Strip out an undesired #if 0 block

As mentioned in discussion of D116821, it's better to just delete this
block than keep it hanging around.

Author: jmorse

llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp

@@ -123,14 +123,6 @@ bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
 }
 
 bool llvm::debuginfoShouldUseDebugInstrRef(const Triple &T) {
-  // Enable by default on x86_64, disable if explicitly turned off on cmdline.
-  // Disabled while https://reviews.llvm.org/D116821 is investigated.
-#if 0
-  if (T.getArch() == llvm::Triple::x86_64 &&
-      ValueTrackingVariableLocations != cl::boolOrDefault::BOU_FALSE)
-    return true;
-#endif
-
-  // Otherwise: enable if explicitly requested on command line.
+  // Enable if explicitly requested on command line.
   return ValueTrackingVariableLocations == cl::boolOrDefault::BOU_TRUE;
 }