Delete CInternalCGUIAccessorBase class from rP31.
Delete GetSetting/SetSetting variants that operate on a GUI page other than the one that the setting is defined in; introduced in rP31, obsolete since rP7214.

Delete CInternalCGUIAccessorBase::GetObjectPointer as these variants were the only caller for that.
Delete CInternalCGUIAccessorBase::HandleMessage from rP144 as it's an unnecessary proxy.
Delete CInternalCGUIAccessorBase::QueryResetting from rP94 by making ResetStates public, equal to UpdateCachedSize from rP77 (public required for VS2015 but not gcc 9).
Move ResetStates to implementation file.

Tested on: gcc 9, VS2015