doc: Remove unnecessary #ifndef Q_QDOC

It was used to prevent qdoc from seeing the entire include
file, but clang qdoc needs to see it.

Change-Id: Ib8dbcdcd68f2003f4dd89ed6a5c9e1b65bc1c67c
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>

src/corelib/kernel/qobjectdefs_impl.h

@@ -38,8 +38,6 @@
 **
 ****************************************************************************/
 
-#ifndef Q_QDOC
-
 #ifndef QOBJECTDEFS_H
 #error Do not include qobjectdefs_impl.h directly
 #include <QtCore/qnamespace.h>
@@ -446,4 +444,3 @@ namespace QtPrivate {
 
 QT_END_NAMESPACE
 
-#endif