fsmonitor: fix hashmap memory leak in fsmonitor_run_daemon

fsmonitor: fix hashmap memory leak in fsmonitor_run_daemon

The `state.cookies` hashmap is initialized during daemon startup but
never freed during cleanup in the `done:` label of
fsmonitor_run_daemon().  The cookie entries also have names allocated
via strbuf_detach() that must be freed individually.

Iterate the hashmap to free each cookie name, then call
hashmap_clear_and_free() to release the entries and table.

Signed-off-by: Paul Tarjan <github@paulisageek.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>