Do not manually dissect OP_TYPE operations

Do not manually dissect OP_TYPE operations

Some code in GDB will examine the structure of an expression to see if
it starts with OP_TYPE, and then proceed to extract the type by hand.

There is no need to do this dissection manually.  evaluate_type does
the same thing via an "allowed" API.

This patch changes such code to use evaluate_type.  In two cases this
simplifies the code.

Regression tested on x86-64 Fedora 28.

gdb/ChangeLog
2020-12-14  Tom Tromey  <tom@tromey.com>

	* dtrace-probe.c (dtrace_process_dof_probe): Use value_type.
	* typeprint.c (whatis_exp): Always use evaluate_type.
	(maintenance_print_type): Likewise.  Simplify.