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/comics_view_transition.cpp

@@ -20,11 +20,6 @@ ComicsViewTransition::ComicsViewTransition(QWidget *parent)
 #endif
 }
 
-QSize ComicsViewTransition::sizeHint()
-{
-    return QSize(450, 350);
-}
-
 void ComicsViewTransition::paintEvent(QPaintEvent *)
 {
     QPainter painter(this);