Remove docs about deploying ffmpegsumo.dll as this is no longer needed

Change-Id: I37adcbff5b1279cf2432189ae8ae6b5e539fda77
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/webengine/doc/src/qtwebengine-deploying.qdoc

@@ -141,11 +141,4 @@
             directory specified by
             QLibraryInfo::location(QLibraryInfo::TranslationsPath)
     \endlist
-
-    \section2 Deploying Audio and Video Codecs
-
-    To support HTML5 video, you must additionally deploy
-    \c ffmpegsumo.dll (WebM codec plugin) into the \c qtwebengine directory
-    under the application install path or under the path that the
-    \c PluginsPath variable was set to in \c qt.conf.
 */