Use htab_up in typedef_hash_table

Use htab_up in typedef_hash_table

This changes typedef_hash_table to use htab_up rather than explicit
calls to htab_delete.

gdb/ChangeLog
2020-09-17  Tom Tromey  <tom@tromey.com>

	* typeprint.h (class typedef_hash_table) <~typedef_hash_table>:
	Remove.
	<m_table>: Now htab_up.
	* typeprint.c (typedef_hash_table::recursively_update)
	(typedef_hash_table::add_template_parameters)
	(typedef_hash_table::typedef_hash_table): Update.
	(typedef_hash_table::~typedef_hash_table): Remove.
	(typedef_hash_table::typedef_hash_table)
	(typedef_hash_table::find_global_typedef)
	(typedef_hash_table::find_typedef): Update.