Remove eIs(Getting|Saving)ViaShuttle enum values...

... Because:

1 They weren't used

2 The branches selected by them were wrongly passing user-visible prompt strings
to DoDataShuttle, which elsewhere takes a preference path (this is an error that
could have been detected and avoided if there weren't naked wxString arguments)

3 Without those branches, the affected Tie... functions become more parallel to
other ShuttleGui member functions, which might later be unified into fewer
functions

src/ShuttleGui.h

@@ -36,8 +36,6 @@ enum teShuttleMode
    eIsCreating,
    eIsGettingFromDialog,
    eIsSettingToDialog,
-   eIsSavingViaShuttle,
-   eIsGettingViaShuttle,
    eIsGettingMetadata,
 
    // Next two are only ever seen in constructor.