Revert "clover: Fix build after llvm r221375"

This reverts commit cd93d82ba9.

llvm r221375 was reverted, so this commit needs to be too.

src/gallium/state_trackers/clover/llvm/invocation.cpp

@@ -282,11 +282,7 @@ namespace {
 
       for (unsigned i = 0; i < kernel_node->getNumOperands(); ++i) {
          kernels.push_back(llvm::dyn_cast<llvm::Function>(
-#if HAVE_LLVM >= 0x0306
-                                    kernel_node->getOperandAsMDNode(i)->getOperand(0)));
-#else
                                     kernel_node->getOperand(i)->getOperand(0)));
-#endif
       }
    }