Do not delete device record on HCI_ERR_KEY_MISSING

If an auth_complete event is received with HCI_ERR_KEY_MISSING, the
p_dev_rec->sm4 flag will be set to "BTM_SM4_UNKNOWN" in the
BTM_SecClearSecurityFlags() function. This will prevent the
BTM_SM4_RETRY procedure from being executed, which can cause
pairing failures.

To reproduce:
 1. Two Phones, A: Android O, B: Android N.
 2. Enable B in Bluetooth visable mode
 3. A start discovery and create pairing with B successfully
 4. B cancel pairing with A by remove A from pairing device
    list of B.
 5. A create paring with B again by touch paired device in A,
    this first step will be failed.

Bug: 62615213
Test: manual
Change-Id: I514ba2f4d0fd2621c11bd83aeec24b8c6c6d2d5a
Signed-off-by: Yequan Song <songyequan@huawei.com>