All SELinux domains are already granted the ability to read the
filenames in /proc, so it's unnecessary to add it to storaged.te.

  $ grep "proc:dir r_dir_perms" public/domain.te
  allow domain proc:dir r_dir_perms;

Remove redundant rule.

Test: policy compiles.
Change-Id: I8779cda19176f7eb914778f131bb5b14e5b14448