Drop shell from having access to dmesg

In normal, user builds, shell doesn't have the required
DAC permissions to acess the kernel log.

Change-Id: I001e6d65f508e07671bdb71ca2c0e1d53bc5b970

shell.te

@@ -19,12 +19,6 @@ allow shell sdcard:file create_file_perms;
 r_dir_file(shell, apk_data_file)
 allow shell dalvikcache_data_file:file write;
 
-# Run dmesg.
-allow shell kernel:system syslog_read;
-
-# Run cat /proc/kmsg.
-allow shell kernel:system syslog_mod;
-
 # Run logcat.
 allow shell log_device:chr_file r_file_perms;