Restore test-cp-name-parser build

Restore test-cp-name-parser build

Commit c8b23b3f89fbb0 ("Add constructor and destructor to
demangle_parse_info") a while ago broke the "test-cp-name-parser"
build:

 $ make test-cp-name-parser
 [...]
 src/gdb/cp-name-parser.y: In function ‘int main(int, char**)’:
 src/gdb/cp-name-parser.y:2190:9: error: cannot convert ‘std::unique_ptr<demangle_parse_info>’ to ‘demangle_parse_info*’ in assignment
   result = cp_demangled_name_to_comp (str2, &errmsg);
	  ^
 src/gdb/cp-name-parser.y:2199:38: error: ‘cp_demangled_name_parse_free’ was not declared in this scope
   cp_demangled_name_parse_free (result);
				       ^
 src/gdb/cp-name-parser.y:2211:14: error: cannot convert ‘std::unique_ptr<demangle_parse_info>’ to ‘demangle_parse_info*’ in assignment
	result = cp_demangled_name_to_comp (argv[arg], &errmsg);
	       ^
 src/gdb/cp-name-parser.y:2219:43: error: ‘cp_demangled_name_parse_free’ was not declared in this scope
	cp_demangled_name_parse_free (result);
					    ^
 Makefile:2107: recipe for target 'test-cp-name-parser.o' failed
 make: *** [test-cp-name-parser.o] Error 1

This commit restores it.

gdb/ChangeLog:
2017-03-14  Pedro Alves  <palves@redhat.com>

	* cp-name-parser.y (cp_demangled_name_to_comp): Update comment.
	(main): Use std::unique_ptr.  Remove calls to
	cp_demangled_name_parse_free.