Validation: remove unused gradient and barrier op collecting

[tex3d]

These gradientOps and barriers sets are unused:

DirectXShaderCompiler/lib/DxilValidation/DxilValidation.cpp

Lines 2642 to 2643 in d5951b7

	SmallVector<CallInst *, 16> gradientOps;
	SmallVector<CallInst *, 16> barriers;

Other than collecting operations into them:

DirectXShaderCompiler/lib/DxilValidation/DxilValidation.cpp

Lines 2722 to 2728 in d5951b7

	if (OP::IsDxilOpGradient(dxilOpcode)) {
	gradientOps.push_back(CI);
	}
	if (dxilOpcode == DXIL::OpCode::Barrier) {
	barriers.push_back(CI);
	}

They look like they were meant to be used for something, but there is no code using them, so they should be removed.