Fix generated documentation for wxZipEntry::GetInternalName()

Remove the group around it to avoid problems due to the existence of
another overload.

This completes the changes of ca59d38cfd (Add missing static to
wxZipEntry::GetInternalName() documentation, 2020-05-25).

Closes https://github.com/wxWidgets/wxWidgets/pull/1876

interface/wx/zipstrm.h

@@ -301,7 +301,6 @@ public:
     */
     int GetFlags() const;
 
-    //@{
     /**
         A static member that translates a filename into the internal format used
         within the archive. If the third parameter is provided, the bool pointed
@@ -321,7 +320,6 @@ public:
         This gives a canonical name that can be used in comparisons.
     */
     wxString GetInternalName() const;
-    //@}
 
     /**
         Returns @true if GetSystemMadeBy() is a flavour of unix.