doc/chapters/api.texi: remove doc for inexisting function

doc/chapters/api.texi

@@ -3395,10 +3395,6 @@ to it.
 Returns the last value set by @code{starpu_data_set_rank}.
 @end deftypefun
 
-@deftypefun starpu_data_handle_t starpu_data_get_data_handle_from_tag (int @var{tag})
-Returns the data handle associated to the MPI tag, or NULL if there is not.
-@end deftypefun
-
 @defmac STARPU_EXECUTE_ON_NODE
 this macro is used when calling @code{starpu_mpi_insert_task}, and
 must be followed by a integer value which specified the node on which