Revert "Cocoa (OpenGL): If no view is attached, makeCurrent() should return false"

This reverts commit 2eb1e28a90,
which makes several of the OpenGL examples crash on startup.
(textures, hellogl_es2)

Change-Id: Id47d2df6f57b2396c333e478b3c062f4cb4becb5
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>

src/plugins/platforms/cocoa/qcocoaglcontext.mm

@@ -182,8 +182,6 @@ bool QCocoaGLContext::makeCurrent(QPlatformSurface *surface)
     QWindow *window = static_cast<QCocoaWindow *>(surface)->window();
     setActiveWindow(window);
 
-    if (![m_context view])
-        return false;
     [m_context makeCurrentContext];
     update();
     return true;