Remove unused bufferhub sepolicy

These selinux policy rules were added for bufferhub to run a binder
service. But later we decided to use a hwbinder service instead, and the
original binder service was removed in git/master. Now we can safely
remove these rules.

Test: Build passed. Device boot successfully without selinux denial.
Bug: 118891412
Change-Id: I349b5f0f2fa8fb6a7cfe7869d936791355c20753