AMDGPU: Remove special case of SGPR_LO class in imm folding (#155518)

Previous change accidentally broke this which shows it's not
doing anything.

Author: arsenm

llvm/lib/Target/AMDGPU/SIFoldOperands.cpp

@@ -1260,14 +1260,6 @@ void SIFoldOperandsImpl::foldOperand(
       return;
 
     const TargetRegisterClass *DestRC = TRI->getRegClassForReg(*MRI, DestReg);
-    // Allow immediates COPYd into sgpr_lo16 to be further folded while
-    // still being legal if not further folded
-    if (DestRC == &AMDGPU::SGPR_LO16RegClass) {
-      assert(ST->useRealTrue16Insts());
-      MRI->setRegClass(DestReg, &AMDGPU::SGPR_32RegClass);
-      DestRC = &AMDGPU::SGPR_32RegClass;
-    }
-
     // In order to fold immediates into copies, we need to change the copy to a
     // MOV. Find a compatible mov instruction with the value.
     for (unsigned MovOp :