Make gdb.mi/user-selected-context-sync.exp use proc_with_prefix

Make gdb.mi/user-selected-context-sync.exp use proc_with_prefix

Pedro's patch provides a cleaner way to prefix tests with the proc name,
so let's use that.

gdb/testsuite/ChangeLog:

	* gdb.mi/user-selected-context-sync.exp (with_test_prefix_procname):
	Remove.
	(test_setup): Define with proc_with_prefix.
	(test_cli_inferior): Likewise.
	(test_cli_thread): Likewise.
	(test_cli_frame): Likewise.
	(test_cli_select_frame): Likewise.
	(test_cli_up_down): Likewise.
	(test_mi_thread_select): Likewise.
	(test_mi_stack_select_frame): Likewise.
	(test_cli_in_mi_inferior): Likewise.
	(test_cli_in_mi_thread): Likewise.
	(test_cli_in_mi_frame): Likewise.
	(top level): Do not use with_test_prefix_procname.