[testsuite/gdb.ada] simplify some testcases by using clean_restart.

[testsuite/gdb.ada] simplify some testcases by using clean_restart.

gdb/testsuite/ChangeLog:

        * gdb.ada/array_bounds.exp, gdb.ada/array_return.exp,
        gdb.ada/array_subscript_addr.exp, gdb.ada/arrayidx.exp,
        gdb.ada/arrayparam.exp, gdb.ada/arrayptr.exp,
        gdb.ada/atomic_enum.exp, gdb.ada/call_pn.exp,
        gdb.ada/catch_ex.exp, gdb.ada/char_param.exp,
        gdb.ada/complete.exp, gdb.ada/exprs.exp, gdb.ada/fixed_cmp.exp,
        gdb.ada/fixed_points.exp, gdb.ada/formatted_ref.exp,
        gdb.ada/frame_args.exp, gdb.ada/fun_addr.exp,
        gdb.ada/fun_in_declare.exp, gdb.ada/funcall_param.exp,
        gdb.ada/homonym.exp, gdb.ada/int_deref.exp,
        gdb.ada/interface.exp, gdb.ada/lang_switch.exp,
        gdb.ada/mod_from_name.exp, gdb.ada/nested.exp,
        gdb.ada/null_array.exp, gdb.ada/null_record.exp,
        gdb.ada/packed_array.exp, gdb.ada/packed_tagged.exp,
        gdb.ada/print_chars.exp, gdb.ada/print_pc.exp,
        gdb.ada/ptype_field.exp, gdb.ada/ptype_tagged_param.exp,
        gdb.ada/rec_return.exp, gdb.ada/ref_param.exp,
        gdb.ada/ref_tick_size.exp, gdb.ada/start.exp,
        gdb.ada/str_ref_cmp.exp, gdb.ada/sym_print_name.exp,
        gdb.ada/taft_type.exp, gdb.ada/tagged.exp, gdb.ada/tasks.exp,
        gdb.ada/tick_last_segv.exp, gdb.ada/type_coercion.exp,
        gdb.ada/uninitialized_vars.exp,
        gdb.ada/variant_record_packed_array.exp, gdb.ada/watch_arg.exp:
        Simplify by using clean_restart.