Remove unused sizeHint() from GridComicsView and ComicsViewTransition

QWidget::sizeHint() is const-qualified, so Clang warns that non-const
sizeHint() member functions merely hide the virtual function of the base
class.

664dac3401 and
9f53ae6efc introduced these member
functions in 2014 without const qualifiers. QWidget::sizeHint() was
const-qualified even in Qt 3. Since these member functions have never
had any effect, they should be removed rather than const-qualified to
preserve the long-standing behaviors of the two classes.

Add a TODO for a similar but less straightforward issue with
PropertiesDialog::sizeHint().

YACReaderLibrary/properties_dialog.h

@@ -122,6 +122,9 @@ public:
     PropertiesDialog(QWidget *parent = nullptr);
     QString databasePath;
     QString basePath;
+    // TODO: this non-const member function hides rather than overrides
+    // QWidget::sizeHint(). But the function cannot be simply removed as it is used
+    // in our constructor. Will have to investigate and decide how to fix this.
     QSize sizeHint();
     void paintEvent(QPaintEvent *event) override;