Revert "Give Zygote the ability to write app data files."

This was a mistaken attempt to fix bug 10498304, but it didn't
actually have any impact. Revert.

This reverts commit fc2bd01b.

Bug: 10498304

zygote.te

@@ -11,9 +11,9 @@ allow zygote self:capability setpcap;
 # Switch SELinux context to app domains.
 allow zygote system_server:process dyntransition;
 allow zygote appdomain:process dyntransition;
-# Allow zygote to read + write app data dirs (b/10455872 and b/10498304)
+# Allow zygote to read app data dirs (b/10455872)
 allow zygote appdomain:dir { getattr search };
-allow zygote appdomain:file { r_file_perms write };
+allow zygote appdomain:file { r_file_perms };
 # Move children into the peer process group.
 allow zygote system_server:process { getpgid setpgid };
 allow zygote appdomain:process { getpgid setpgid };