Because of recent improvements to ddg.c, the reaching uses problem is no
longer used.
I am deleting it because it is not really a useful dataflow problem in
that it tends to be more expensive to compute than reaching defs but
provides little extra information. 

Removing the code will discourage any subsequent usage. 

I bootstrapped this change on x86-64.

Ok for commit?

Kenny



2007-07-31  Kenneth Zadeck <zadeck@naturalbridge.com>

        * df.h (DF_RU, DF_RU_BB_INFO, df_ru_bb_info, df_ru,
    df_ru_add_problem, df_ru_get_bb_info): Removed.
    (DF_RD, DF_UREC, DF_CHAIN, DF_NOTE): Renumbered.
    * df-problems.c (df_ru_problem_data, df_ru_set_bb_info,
    df_ru_free_bb_info, df_ru_alloc,
    df_ru_bb_local_compute_process_def,
    df_ru_bb_local_compute_process_use, df_ru_bb_local_compute,
    df_ru_local_compute, df_ru_init_solution, df_ru_confluence_n,
    df_ru_transfer_function, df_ru_free, df_ru_start_dump,
    df_ru_top_dump, df_ru_bottom_dump, df_problem problem_RU,
    df_ru_add_problem): Removed.