windowscodecs: Remove extern from function definition

[Andrew Talbot]

Changelog:
    windowscodecs: Remove extern from function definition.

diff --git a/dlls/windowscodecs/propertybag.c b/dlls/windowscodecs/propertybag.c
index 43c88c7..128cf24 100644
--- a/dlls/windowscodecs/propertybag.c
+++ b/dlls/windowscodecs/propertybag.c
@@ -136,7 +136,7 @@ static const IPropertyBag2Vtbl PropertyBag_Vtbl = {
     PropertyBag_LoadObject
 };
 
-extern HRESULT CreatePropertyBag2(IPropertyBag2 **ppPropertyBag2)
+HRESULT CreatePropertyBag2(IPropertyBag2 **ppPropertyBag2)
 {
     PropertyBag *This;