Fix 100 LE device connection limitation

Currently after 100 devices are added to the device security database,
any subsequent LE connection to a newly discovered LE device address
will fail as entries in the security record database are not reused.

This patch removes a device record if the device itself is removed and
also ensures that the oldest device security record is deleted if the
limit is reached to ensure a new record can be allocated.

Bug: 31625900
Change-Id: I22f6c82c64a9a9bfb2a16d79182903e5aa011355