edit: Fix libreadline history clearing with WPA_TRACE

edit: Fix libreadline history clearing with WPA_TRACE

The HIST_ENTRY and its variables are allocated within libreadline, so
they won't have the WPA_TRACE special header and cannot be freed with
os_free(). Use free() to avoid issues during wpa_cli termination if any
of the new commands added to the history are to be removed (e.g.,
set_network could include a password).

Signed-hostap: Jouni Malinen <j@w1.fi>