build: clear 227 warnings - dead private fields, malformed comments (#15376)

build: drop dead private fields, close malformed comments (227 warnings)

Clears 227 of the clang-cl warnings tracked in #15374, taking a full
Windows build from 1,491 to 1,264. Five of the six changes are in
headers, which are re-diagnosed in every translation unit that includes
them, so the count is large for a 14-line diff.

Tabbook.hpp: delete two private fields, unread since the 2022 import.
m_parent also shadowed wxWindowBase::m_parent.

GUI_Utils.hpp: the wxEVT_SYS_COLOUR_CHANGED lambda body is empty on
Windows, so its `this` capture is unused there. (void) this; leaves the
handler bound, which is what stops the event propagating.

DevFirmware.h: mark m_owner [[maybe_unused]]. The class is never
instantiated, and the file tracks BambuStudio, so this is the smallest
divergence.

Eight DeviceTab/ files, AMSItem.cpp and SelectMachine.cpp: block
comments malformed so that they read as a nested /*.

No behavior change. -Wcomment goes to zero, and only the three intended
categories move.

src/slic3r/GUI/Tabbook.hpp

@@ -36,7 +36,6 @@ public:
     TabButton*                      pageButton;
 
 private:
-    wxWindow*                       m_parent;
     wxFlexGridSizer*                m_buttons_sizer;
     wxBoxSizer*                     m_sizer;
     ScalableBitmap                  m_arrow_img;
@@ -400,8 +399,6 @@ private:
     unsigned m_showTimeout,
              m_hideTimeout;
 
-    TabButtonsListCtrl *m_ctrl{nullptr};
-
 };
 //#endif // _WIN32
 #endif // slic3r_Tabbook_hpp_