Docs: Update the screenshots for the Qt Widgets examples

This commit updates the screenshots for the Qt Widget examples. It also
removes several unused screenshots and adds several minor edits.

Task-number: QTBUG-69988
Change-Id: I23b90fd6c8b798169d158854609c09ef3f1c1a20
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
(cherry picked from commit 618b1faf37ddda4cdeff6934f5af7e699c9aad63)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/widgets/doc/src/gallery.qdoc

@@ -9,6 +9,8 @@
     \ingroup examples-widgets
     \brief The Widgets Gallery example shows widgets relevant for designing UIs.
 
+    \image gallery-example.png "Screenshot of the example"
+
     This example demonstrates widgets typically used in dialogs and forms.
     It also allows for changing the style.
 */

examples/widgets/doc/src/licensewizard.qdoc

@@ -19,7 +19,7 @@
 
     Some wizards are more complex in that they allow different
     traversal paths based on the information provided by the user.
-    The License Wizard example illustrates this. It provides five
+    The License Wizard example illustrates this. It provides several
     wizard pages; depending on which options are selected, the user
     can reach different pages.
 

src/widgets/dialogs/qwizard.cpp

@@ -1972,7 +1972,7 @@ void QWizardAntiFlickerWidget::paintEvent(QPaintEvent *)
     Some wizards are more complex in that they allow different
     traversal paths based on the information provided by the user.
     The \l{dialogs/licensewizard}{License Wizard} example illustrates this.
-    It provides five wizard pages; depending on which options are
+    It provides several wizard pages; depending on which options are
     selected, the user can reach different pages.
 
     \image licensewizard-flow.png