NFC: Resolve a -Wunused-lambda-capture warning.

Author: tshortli

lib/AST/Module.cpp

@@ -275,7 +275,7 @@ void SourceLookupCache::addToUnqualifiedLookupCache(Range items,
       continue;
 
     if (auto *VD = dyn_cast<ValueDecl>(D)) {
-      auto getDerivative = [onlyDerivatives, VD]() -> AbstractFunctionDecl * {
+      auto getDerivative = [VD]() -> AbstractFunctionDecl * {
         if (auto *AFD = dyn_cast<AbstractFunctionDecl>(VD))
           if (AFD->getAttrs().hasAttribute<DerivativeAttr>())
             return AFD;