Bug 1050174: Cleanup fields in |DroidSocketImpl| (under bluetooth2/), r=btian

|DroidSocketImpl| contains several unused fields that are removed
by this patch.
Bug 1050174: Use |SocketConsumerBase| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIORunnable| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIOEventRunnable| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIOReceiveRunnable| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIORequestClosingRunnable| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIODeleteInstanceRunnable| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIOBase| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIOTask| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIOSendTask| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Use |SocketIOShutdownTask| for Bluetooth sockets (under bluetooth2/), r=btian
Bug 1050174: Cleanup interface of |BluetoothSocket| (under bluetoth2/), r=btian

This patch cleans up the interface of Bluedroid's |BluetoothScoket|
to look more similar the interface of |UnixSocketConsumer|, from
which it descends.