hal: Do not delete DEVICE_CONNECT and DISCONNECT params

BT audio playback is not working as AUDIO_PARAMETER_DEVICE_CONNECT
param string is deleted by FFV module.
Do not delete AUDIO_PARAMETER_DEVICE_CONNECT and
AUDIO_PARAMETER_DEVICE_DISCONNECT strings as they are used by other
modules also.

Change-Id: Ice61399814f5f238afdb76b32bacfc316d839f3f