run-as policy fixes.

- Remove dac_read_search as it is no longer required by run-as.
- Introduce a separate type for /dev/tty so that we can allow use of own tty for
for a run-as shell without allowing access to other /dev/tty[0-9]* nodes.
- Allow sigchld notifications for death of run-as and its descendants by adbd.
- Drop redundant rules for executing shell or system commands from untrusted_app;
now covered by rules in app.te.

Change-Id: Ic3bf7bee9eeabf9ad4a20f61fbb142a64bb37c6c
diff --git a/file_contexts b/file_contexts
index 1e34bd9..ccbb99a 100644
--- a/file_contexts
+++ b/file_contexts
@@ -101,6 +101,7 @@
 /dev/spdif_out.*	u:object_r:audio_device:s0
 /dev/tegra.*		u:object_r:video_device:s0
 /dev/tf_driver		u:object_r:tee_device:s0
+/dev/tty		u:object_r:owntty_device:s0
 /dev/tty[0-9]*		u:object_r:tty_device:s0
 /dev/ttyS[0-9]*		u:object_r:serial_device:s0
 /dev/tun		u:object_r:tun_device:s0