[binutils-gdb] Remove a cleanup from trace_dump_actions

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 15b6611c69f6fdb7a20cd50d33d9acf8c5c32037 ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 15b6611c69f6fdb7a20cd50d33d9acf8c5c32037

Remove a cleanup from trace_dump_actions

This changes trace_dump_actions to use std::string, removing a
cleanup.

Tested by the buildbot.

ChangeLog
2018-05-21  Tom Tromey  <tom@tromey.com>

	* tracepoint.c (trace_dump_actions): Use std::string.