Doc: Made \since command in Dialog QML types consistent.

-QDoc only requires the version number for Qt versions

Task-number: QTBUG-32172
Change-Id: Ifa3a94fa66194807d58b079b4f451af90cc1d00a
Reviewed-by: Martin Smith <martin.smith@digia.com>

src/imports/dialogs/qquickplatformcolordialog.cpp

@@ -55,7 +55,7 @@ QT_BEGIN_NAMESPACE
     \inqmlmodule QtQuick.Dialogs 1
     \ingroup dialogs
     \brief Dialog component for choosing a color.
-    \since Qt 5.1
+    \since 5.1
 
     ColorDialog allows the user to select a color. The dialog is initially
     invisible. You need to set the properties as desired first, then set

src/imports/dialogs/qquickplatformfiledialog.cpp

@@ -55,7 +55,7 @@ QT_BEGIN_NAMESPACE
     \inqmlmodule QtQuick.Dialogs 1
     \ingroup dialogs
     \brief Dialog component for choosing files from a local filesystem.
-    \since Qt 5.1
+    \since 5.1
 
     FileDialog provides a basic file chooser: it allows the user to select
     existing files and/or directories, or create new filenames. The dialog is

src/imports/dialogs/qquickplatformmessagedialog.cpp

@@ -55,7 +55,7 @@ QT_BEGIN_NAMESPACE
     \inqmlmodule QtQuick.Dialogs 1
     \ingroup dialogs
     \brief Dialog component for displaying popup messages.
-    \since Qt 5.2
+    \since 5.2
 
     The most basic use case for a MessageDialog is a popup alert. It also
     allows the user to respond in various ways depending on which buttons are