ANDROID: binder: remove proc waitqueue

Removes the process waitqueue, so that threads
can only wait on the thread waitqueue. Whenever
there is process work to do, pick a thread and
wake it up.

This also fixes an issue with using epoll(),
since we no longer have to block on different
waitqueues.

Bug: 34461621
Change-Id: I2950b9de6fa078ee72d53c667a03cbaf587f0849
Signed-off-by: Martijn Coenen <maco@google.com>