Avoid SElinux denial accessing SIM card lock

This change avoids the following SELinux denial:

  W/SharedPreferenc(28238): type=1400 audit(0.0:8): avc: denied\
  { search } for name="com.android.settings" dev="mmcblk0p25"\
  ino=8209 scontext=u:r:radio:s0 tcontext=u:object_r:system_app\
  _data_file:s0 tclass=dir op_res=-13 ppid=318 pcomm="main"\
  tgid=1850 tgcomm="m.android.phone"

When accessing Settings->Security->Set up SIM card lock.

There is really no need to store this information in
SharedPreferences anyway.

(cherrypicked from commit bef7221a)

Change-Id: I3ba30d5d5e2c5b3c379397fbb06325101acaf490