Remove second QUICHE_EXPORT for SignatureChanger

Since SignatureChanger has already been exported once, the second one causes “'dllexport' attribute ignored [-Werror,-Wignored-attributes]” when rolling quiche to Chromium on a Windows component build. This CL fixes this by removing the second export.

PiperOrigin-RevId: 537455589

quiche/common/quiche_callbacks.h

diff --git a/quiche/common/quiche_callbacks.h b/quiche/common/quiche_callbacks.h
index 15eb1a9..18529eb 100644
--- a/quiche/common/quiche_callbacks.h
+++ b/quiche/common/quiche_callbacks.h
@@ -40,7 +40,7 @@
 class QUICHE_EXPORT SignatureChanger {};
 
 template <typename ReturnType, typename... Args>
-class QUICHE_EXPORT SignatureChanger<ReturnType(Args...)> {
+class QUICHE_NO_EXPORT SignatureChanger<ReturnType(Args...)> {
  public:
   using Rvalue = ReturnType(Args...) &&;
   using Const = ReturnType(Args...) const;