GlobalISel: Remove some mystery code that clears isReturned

[arsenm]

Summary

I don't understand what this is going for, and haven't found an analog
in DAG code. No tests fail with this removed.

[aemerson]

Can't remember exactly what triggered this, so if its not tested then sure.

[arsenm]

904dab55abf637586897f14573bf1182d5001a0e

llvm/lib/CodeGen/GlobalISel/CallLowering.cpp

for (unsigned Part = 0; Part < NumParts; ++Part) {
       if (Part == 0) {
         Flags.setSplit();
       } else {
         Flags.setOrigAlign(Align(1));
         if (Part == NumParts - 1)
           Flags.setSplitEnd();
       }
 
-      if (!Assigner.isIncomingArgumentHandler()) {
-        // TODO: Also check if there is a valid extension that preserves the
-        // bits. However currently this call lowering doesn't support non-exact
-        // split parts, so that can't be tested.
-        if (OrigFlags.isReturned() &&
-            (NumParts * NewVT.getSizeInBits() != CurVT.getSizeInBits())) {
-          Flags.setReturned(false);
-        }
-      }
-
       Args[i].Flags.push_back(Flags);
       if (Assigner.assignArg(i, CurTy, NewVT, NewVT, CCValAssign::Full, Args[i],
                              Args[i].Flags[Part], CCInfo)) {
         // Still couldn't assign this smaller part type for some reason.
         return false;
       }
     }
   }