app: remove redundant neverallow rule

Access to zygote_socket is already neverallowed to
{ domain -system_server }.

Test: build
Change-Id: I6353ef09f769c8d64c97b1bdef93f0ab4d5dae6a

public/app.te

@@ -404,7 +404,6 @@ neverallow appdomain socket_device:sock_file write;
 # Unix domain sockets.
 neverallow appdomain adbd_socket:sock_file write;
 neverallow { appdomain -radio } rild_socket:sock_file write;
-neverallow appdomain zygote_socket:sock_file write;
 
 # ptrace access to non-app domains.
 neverallow appdomain { domain -appdomain }:process ptrace;