Fixed compile of quicktime plugin

This code was including the qmacdefines_mac.h header from QtWidgets,
which has recently been removed.  Using the header is no longer
necessary.

Note that the qmacdefines_mac.h contained a workaround for some mac
system headers declaring variables named `slots'.  Replace that
workaround with the standard no_keywords method.

Change-Id: Icd47a562d64953692e50a9fea8bb4a9c8424375c
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/plugins/plugins.pro

@@ -35,10 +35,6 @@ unix:!mac {
 }
 
 mac:!simulator {
-    SUBDIRS += audiocapture
-
-    # Currently we need qmacdefines_mac.h from QtWidgets, so this depends on that :/
-    # despite the code not really using them.
-    !isEmpty(QT.widgets.name):SUBDIRS += qt7
+    SUBDIRS += audiocapture qt7
 }