Update platformheaders docs about bc.

Remove the "As of Qt 5.4" to avoid misunderstandings.
Also add the note for the classes that miss it.

Change-Id: Id7f437954bb3ec12c0fc944c18e58e6e977863f1
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

src/platformheaders/eglfsfunctions/qeglfsfunctions.qdoc

@@ -32,6 +32,10 @@
     \brief The QEglFSFunctions class is an inline class containing
     platform-specific functionality for the eglfs platform plugin that is
     typically used on systems running Embedded Linux or Android.
+
+    \note There is no binary compatibility guarantee for this class,
+    meaning that an application using it is only guaranteed to work with the Qt
+    version it was developed against.
 */
 
 /*!

src/platformheaders/nativecontexts/qeglnativecontext.qdoc

@@ -32,7 +32,7 @@
 
   \brief A class encapsulating an EGL context and display handle
 
-  \note As of Qt 5.4 there is no binary compatibility guarantee for this class, meaning
+  \note There is no binary compatibility guarantee for this class, meaning
   that an application using it is only guaranteed to work with the Qt version it was
   developed against.
 

src/platformheaders/nativecontexts/qglxnativecontext.qdoc

@@ -39,7 +39,7 @@
   fail. For modern contexts created with an FBConfig, these are not necessary, the
   GLXContext itself is sufficient. The Display is optional.
 
-  \note As of Qt 5.4 there is no binary compatibility guarantee for this class, meaning
+  \note There is no binary compatibility guarantee for this class, meaning
   that an application using it is only guaranteed to work with the Qt version it was
   developed against.
 

src/platformheaders/nativecontexts/qwglnativecontext.qdoc

@@ -32,7 +32,7 @@
 
   \brief A class encapsulating a WGL context on Windows with desktop OpenGL (opengl32.dll)
 
-  \note As of Qt 5.4 there is no binary compatibility guarantee for this class,
+  \note There is no binary compatibility guarantee for this class,
   meaning that an application using it is only guaranteed to work with the Qt
   version it was developed against.
 

src/platformheaders/xcbfunctions/qxcbwindowfunctions.qdoc

@@ -34,6 +34,10 @@
 
     A commen usage pattern is as follows:
     \snippet qxcbwindowfunctions/main.cpp 0
+
+    \note There is no binary compatibility guarantee for this class,
+    meaning that an application using it is only guaranteed to work with the Qt
+    version it was developed against.
 */
 
 /*!