Fix the BLE connection failure with some mice

If enable the "connection parameters update" during GATT discovery,
it may cause some device connection failure due to connection timeout.
Since the the "connection parameter update" is enabled again when GATT
discovery completed, remove the enable of "connection parameter update"
after SMP complete to fix the issue.

This issue was already fixed in commit e3466c35, but then it was
re-introduced in commit 29c725d4, which also removed comment explaining
the issue, added back in this patch.

Bug: 29060797
Change-Id: I42b0b36056821c30d887484e22bfcbd04ea7ca03