keymaster 3.0: make service use nobody as user and remove system group

Only the drmrpc group is necessary

Test: VtsHalKeymasterV3_0TargetTest
Change-Id: I2be255215df827c9f17ecaffcb9d0ba402dd3405
diff --git a/keymaster/3.0/default/android.hardware.keymaster@3.0-service.rc b/keymaster/3.0/default/android.hardware.keymaster@3.0-service.rc
index 086ba2f..ea8d490 100644
--- a/keymaster/3.0/default/android.hardware.keymaster@3.0-service.rc
+++ b/keymaster/3.0/default/android.hardware.keymaster@3.0-service.rc
@@ -1,4 +1,4 @@
 service vendor.keymaster-3-0 /vendor/bin/hw/android.hardware.keymaster@3.0-service
     class early_hal
-    user system
-    group system drmrpc
+    user nobody
+    group drmrpc