Remove cleanups from linespec.c

Remove cleanups from linespec.c

This removes the remaining cleanups from linespec.c.  This adds a
constructor and destructor to linespec_parser, but in a minimal way --
the parser could still benefit from a bit more C++-ification.

gdb/ChangeLog
2019-01-02  Tom Tromey  <tom@tromey.com>

	* linespec.c (struct linespec_parser): Rename from ls_parser.  Add
	constructor, destructor.
	(linespec_parser): Remove typedef.
	(~linespec_parser): Rename from linespec_parser_delete.
	(linespec_lex_to_end, linespec_complete_label)
	(linespec_complete): Update.
	(decode_line_full): Remove cleanups.
	(decode_line_1): Update.