tests: Fix ap-mgmt-fuzzer exit to free memory

tests: Fix ap-mgmt-fuzzer exit to free memory

This fuzzing wrapper does not go through full hostapd_clean_iface() call
to free memory, so call ap_list_deinit() to avoid reporting memory leaks
from added AP list entries. This case could not be hit with
hostapd/wpa_supplicant since they perform full interface deinit on
interface removal.

Credit to OSS-Fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=14928
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>