Doc: reflect change in the UI

Update text and screenshots after the Link QML debugging library
check box label was removed and Enable QML debugging label is
always used.

Task-number: QTCREATORBUG-6541
Change-Id: Id53f5db2b9007a2e3c7b939cae61073b519fdb18
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

doc/src/debugger/qtquick-debugging.qdoc

@@ -62,8 +62,9 @@
 
         \list 1
 
-        \o  Select \gui Projects, and then select the \gui {Link QML debugging
-            library} check box in \gui {Build Steps}.
+        \o  Select \gui Projects, and then select the
+            \gui {Enable QML debugging} check box in the \gui qmake section
+            in \gui {Build Steps}.
 
             You might have to compile the library first, by selecting the
             \gui Compile link.