Remove recently added GetOpenGLScaleFactor()

It has become unnecessary after the previous commit, as now the generic
GetContentScaleFactor() can be used instead of it on all platforms, so
revert the changes of f6cc8ff52c (Add GetOpenGLScaleFactor() to abstract
OpenGL coordinates scaling, 2020-07-10).

See https://github.com/wxWidgets/wxWidgets/pull/1944

See #17391.

samples/opengl/cube/cube.cpp

@@ -349,7 +349,7 @@ void TestGLCanvas::OnPaint(wxPaintEvent& WXUNUSED(event))
     // multiple canvases: If we updated the viewport in the wxSizeEvent
     // handler, changing the size of one canvas causes a viewport setting that
     // is wrong when next another canvas is repainted.
-    const wxSize ClientSize = GetClientSize() * GetOpenGLScaleFactor();
+    const wxSize ClientSize = GetClientSize() * GetContentScaleFactor();
 
     TestGLContext& canvas = wxGetApp().GetContext(this, m_useStereo);
     glViewport(0, 0, ClientSize.x, ClientSize.y);

samples/opengl/isosurf/isosurf.cpp

@@ -280,7 +280,7 @@ void TestGLCanvas::OnSize(wxSizeEvent& event)
     // This is OK here only because there is only one canvas that uses the
     // context. See the cube sample for that case that multiple canvases are
     // made current with one context.
-    const wxSize size = event.GetSize() * GetOpenGLScaleFactor();
+    const wxSize size = event.GetSize() * GetContentScaleFactor();
     glViewport(0, 0, size.x, size.y);
 }
 

samples/opengl/penguin/penguin.cpp

@@ -306,7 +306,7 @@ void TestGLCanvas::ResetProjectionMode()
     // or more than one wxGLContext in the application.
     SetCurrent(*m_glRC);
 
-    const wxSize ClientSize = GetClientSize() * GetOpenGLScaleFactor();
+    const wxSize ClientSize = GetClientSize() * GetContentScaleFactor();
 
     // It's up to the application code to update the OpenGL viewport settings.
     // In order to avoid extensive context switching, consider doing this in

samples/opengl/pyramid/pyramid.cpp

@@ -565,7 +565,7 @@ void MyGLCanvas::OnSize(wxSizeEvent& event)
     SetCurrent(*m_oglContext);
 
     // It's up to the application code to update the OpenGL viewport settings.
-    const wxSize size = event.GetSize() * GetOpenGLScaleFactor();
+    const wxSize size = event.GetSize() * GetContentScaleFactor();
     m_winHeight = size.y;
     m_oglManager->SetViewport(0, 0, size.x, m_winHeight);