shdocvw: Remove unneeded cast

[Andrew Talbot]

Changelog:
    shdocvw: Remove unneeded cast.

diff --git a/dlls/shdocvw/navigate.c b/dlls/shdocvw/navigate.c
index ad9fc0b..98f1c58 100644
--- a/dlls/shdocvw/navigate.c
+++ b/dlls/shdocvw/navigate.c
@@ -613,7 +613,7 @@ static HRESULT navigate_mon(DocHost *This, IMoniker *mon, PBYTE post_data, ULONG
     CoTaskMemFree(This->url);
     This->url = url;
 
-    callback = create_callback(This, post_data, post_data_len, (LPWSTR)headers);
+    callback = create_callback(This, post_data, post_data_len, headers);
     CreateAsyncBindCtx(0, callback, 0, &bindctx);
 
     hres = bind_to_object(This, mon, This->url, bindctx, callback);