Remove unused support for target-based exception catching.

Remove unused support for target-based exception catching.
* target.h (struct target_ops): Delete
to_enable_exception_callback and to_get_current_exception_event
members.
(target_enable_exception_callback)
(target_get_current_exception_event): Delete macros.
* target.c (update_current_target): Remove code to inherit and
default those members.
(debug_to_enable_exception_callback)
(debug_to_get_current_exception_event): Delete functions.
(setup_target_debug): Don't install those methods.
* inf-child.c (inf_child_enable_exception_callback)
(inf_child_get_current_exception_event): Delete dummy functions.
(inf_child_target): Don't install them in the target vector.
* breakpoint.h (enum bptype): Delete bp_catch_catch,
bp_catch_throw.
* breakpoint.c (cover_target_enable_exception_callback)
(ep_is_exception_catchpoint, create_exception_catchpoint): Delete
functions.
(insert_bp_location, update_breakpoints_after_exec)
(remove_breakpoint, ep_is_catchpoint, print_it_typical)
(bpstat_stop_status, bpstat_what)
(bpstat_get_triggered_catchpoints, print_one_breakpoint_location)
(user_settable_breakpoint, allocate_bp_location)
(disable_watchpoints_before_interactive_call_start)
(enable_watchpoints_after_interactive_call_stop, mention)
(delete_breakpoint, breakpoint_re_set_one, disable_command)
(enable_command): Remove exception catchpoint cases.
(catch_exception_command_1): Don't try target-based exception
handling.
* stack.c (catch_info): Call print_frame_label_vars
unconditionally.