Remove unnecessary captures in toWasmValType

PR llvm#147486 broke the sanitizer buildbot. These captures were needed
when toWasmValType emitted a diagnostic but are no longer needed
since we changed it to an assertion failure.
This removes the unneeded captures and should fix the sanitizer-buildbot.

Author: hoodmane

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

@@ -123,7 +123,7 @@ static SDValue getTagSymNode(int Tag, SelectionDAG *DAG) {
 static APInt encodeFunctionSignature(SelectionDAG *DAG, SDLoc &DL,
                                      SmallVector<MVT, 4> &Returns,
                                      SmallVector<MVT, 4> &Params) {
-  auto toWasmValType = [&](MVT VT) {
+  auto toWasmValType = [](MVT VT) {
     if (VT == MVT::i32) {
       return wasm::ValType::I32;
     }