The has_more predicate in remote_target::download_tracepoint always
evaluates to true, so the last action packet will be sent with a
trailing '-'.  This patch changes the predicate to remove the last
trailing '-'.

gdb/ChangeLog:
2018-08-06  Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* remote.c (remote_target::download_tracepoint): Fix the has_more
	predicate in the QTDP action list iteration.