Remove support for catch load and catch unload commands.

    Remove support for catch load and catch unload commands.

        * breakpoint.h (enum bptype): Remove bp_catch_load and bp_catch_unload.
        (struct breakpoint): Remove fields dll_pathname and
        triggered_dll_pathname.
        (bpstat_get_triggered_catchpoints, ep_is_shlib_catchpoint): Delete.
        * breakpoint.c (ep_is_catchpoint): Remove handling of
        bp_catch_load and bp_catch_unload.
        (print_it_typical, bpstat_check_location, bpstat_what)
        (print_one_breakpoint_location, print_one_breakpoint_location)
        (user_settable_breakpoint, allocate_bp_location)
        (set_raw_breakpoint_without_location, mention, delete_breakpoint,
        (breakpoint_re_set_one, disable_command, enable_command): Likewise.
        (ep_is_shlib_catchpoint, bpstat_get_triggered_catchpoints)
        (catch_load_command_1, catch_unload_command_1): Delete.
        (_initialize_breakpoint): Remove the "catch load" and "catch unload"
        command creation.
        * infrun.c (handle_inferior_event): Remove the handling of
        load/unload catchpoint events.