Revert "OS X: main window doesn't become key."

This reverts commit da0c74550f.
The patch da0c74 unfortunately does not work well with QCocoaMenuBar's logic:
it can happen that our selectNextKeyWindow chooses a Popup or another window with
some 'unusual' flag as a key, but QCocoaMenuBar::updateMenuBarImmediately will return
immediately, assuming that popup does not have a menu and there are no menu items to enable.

Task-number: QTBUG-44369
Change-Id: I83cd2f6a62acd3a6ceb4d9dbf53ca42af67476d8
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -82,31 +82,6 @@ static bool isMouseEvent(NSEvent *ev)
     }
 }
 
-static void selectNextKeyWindow(NSWindow *currentKeyWindow)
-{
-    if (!currentKeyWindow)
-        return;
-
-    const QCocoaAutoReleasePool pool;
-
-    if ([[NSApplication sharedApplication] keyWindow] != currentKeyWindow)
-        return;//currentKeyWindow is not a key window actually.
-
-    NSArray *const windows = [[NSApplication sharedApplication] windows];
-    bool startLookup = false;
-    for (NSWindow *candidate in [windows reverseObjectEnumerator]) {
-        if (!startLookup) {
-            if (candidate == currentKeyWindow)
-                startLookup = true;
-        } else {
-            if ([candidate isVisible] && [candidate canBecomeKeyWindow]) {
-                [candidate makeKeyWindow];
-                break;
-            }
-        }
-    }
-}
-
 @implementation QNSWindowHelper
 
 @synthesize window = _window;
@@ -599,9 +574,6 @@ void QCocoaWindow::hide(bool becauseOfAncestor)
     foreach (QCocoaWindow *childWindow, m_childWindows)
         childWindow->hide(true);
 
-    if (window()->transientParent() && m_nsWindow == [[NSApplication sharedApplication] keyWindow])
-        selectNextKeyWindow(m_nsWindow); // Otherwise, Cocoa can do it wrong.
-
     [m_nsWindow orderOut:nil];
 }