[RemoveDIs] Remove unused debug-printing facility for DPMarkers

We originally thought that printing the DPMarker pointer after each
instruction was going to be useful, but it turns out it only serves to
generate spurious test output differences now. As it stands, the cannonical
way to debug RemoveDIs metadata is "dumpDbgValues".

Author: jmorse

llvm/lib/IR/AsmWriter.cpp

@@ -4092,12 +4092,6 @@ void AssemblyWriter::printInfoComment(const Value &V) {
 
   if (AnnotationWriter) {
     AnnotationWriter->printInfoComment(V, Out);
-  } else if (const Instruction *I = dyn_cast<Instruction>(&V)) {
-    if (I->DbgMarker) {
-      // In the new, experimental DPValue representation of debug-info, print
-      // out which instructions have DPMarkers and where they are.
-      Out << "; dbgmarker @ " << I->DbgMarker;
-    }
   }
 }