Stop omitted enum value from showing up in Qt namespace doc.

The following omitted enum description can be seen at [1]:

"Ensures that the longest variant is always used when computing the
size of a multi-variant string. (Internal)"

This is because \omitvalue does not allow a description (whereas
\value does).

The description was moved to the qnamespace.h as a code comment.

[1] http://qt-project.org/doc/qt-5/qt.html#TextFlag-enum

Change-Id: I7983613bffa90f3071a4e2d678696391048c8757
Reviewed-by: Martin Smith <martin.smith@digia.com>

src/corelib/global/qnamespace.h

@@ -267,6 +267,8 @@ public:
         TextJustificationForced = 0x10000,
         TextForceLeftToRight = 0x20000,
         TextForceRightToLeft = 0x40000,
+        // Ensures that the longest variant is always used when computing the
+        // size of a multi-variant string.
         TextLongestVariant = 0x80000,
         TextBypassShaping = 0x100000
     };

src/corelib/global/qnamespace.qdoc

@@ -493,8 +493,7 @@
            text; otherwise this width is excluded.
     \value TextJustificationForced Ensures that text lines are justified.
 
-    \omitvalue TextLongestVariant Ensures that the longest variant is always used
-           when computing the size of a multi-variant string. (Internal)
+    \omitvalue TextLongestVariant
     \omitvalue TextBypassShaping
     \omitvalue TextForceLeftToRight
     \omitvalue TextForceRightToLeft