Remove unused testing hooks in WinWebAuthnApi

This is a follow up to https://crrev.com/c/1789751 that removes the unused testing hooks for the fake WinWebAuthnApi since the fake is now injected via the FidoDiscoveryFactory

Change-Id: Iadfc043d0836e7640e75981c4d49e59c2d079c5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815880
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#698780}

device/fido/win/webauthn_api.cc

@@ -162,30 +162,12 @@ class WinWebAuthnApiImpl : public WinWebAuthnApi {
   decltype(&WebAuthNGetApiVersionNumber) get_api_version_number_ = nullptr;
 };
 
-static WinWebAuthnApi* kDefaultForTesting = nullptr;
-
 // static
 WinWebAuthnApi* WinWebAuthnApi::GetDefault() {
-  if (kDefaultForTesting) {
-    return kDefaultForTesting;
-  }
-
   static base::NoDestructor<WinWebAuthnApiImpl> api;
   return api.get();
 }
 
-// static
-void WinWebAuthnApi::SetDefaultForTesting(WinWebAuthnApi* api) {
-  DCHECK(!kDefaultForTesting);
-  kDefaultForTesting = api;
-}
-
-// static
-void WinWebAuthnApi::ClearDefaultForTesting() {
-  DCHECK(kDefaultForTesting);
-  kDefaultForTesting = nullptr;
-}
-
 WinWebAuthnApi::WinWebAuthnApi() = default;
 
 WinWebAuthnApi::~WinWebAuthnApi() = default;

device/fido/win/webauthn_api.h

@@ -70,11 +70,6 @@ class COMPONENT_EXPORT(DEVICE_FIDO) WinWebAuthnApi {
 
  protected:
   WinWebAuthnApi();
-
- private:
-  friend class ScopedFakeWinWebAuthnApi;
-  static void SetDefaultForTesting(WinWebAuthnApi* api);
-  static void ClearDefaultForTesting();
 };
 
 std::pair<CtapDeviceResponseCode,