Clear BLE block from device records at unpair

Use Case:
Pair and unpair LE remote device repeatedly. The repair
intermittently fails with the error "DHKey Check Failure"

Failure:
Pairing failure is observed when pairing is performed
after unpairing, without performing a BT reset.
Further analysis of the SMP logs indicate that DUT uses the
static address of the remote device for calculation of the
MacKey value. At the time of pairing, the remote RPA should
be used (and the static address has not yet been distributed either).
The problem is caused by the previous dev record which is left in
the stack, and at the time of repair, stack picks the old device
record and reuses it.

Fix:
This change removes the entire BLE block from the device record,
after the unpairing is performed, so that a new device record
is allocated, after the repairing is done.

Bug: 27852645
Change-Id: I8d605d1bb3b1c32061a8d8a7a7fe0fe200030abc