migration: Remove item on pools with different media types.

This was already said in the previous section (see also the first item).

manuals/en/main/migration.tex

@@ -119,10 +119,6 @@ \section{Important Migration Considerations}
       still defined in the current director configuration. Otherwise
       you'll get a fatal error.
 
-\item If you keep Volumes of different Media Types in the same Pool,
-      it is not clear how well migration will work.  We recommend only
-      one \linkResourceDirective{Dir}{Storage}{Media Type} per pool.
-
 \item It is possible to get into a resource deadlock where Bareos does
       not find enough drives to simultaneously read and write all the
       Volumes needed to do Migrations. For the moment, you must take