Revert "Enabled Joe's rcu instead of preempt rcu subsystem"

This reverts commit 389591b1f980e98c78e4c9c37a1fb4095c1746d2.
Revert "Manually patched to add RCU: Joe's RCU."

This reverts commit f05bdd4c8e2c17d9660591d5faded50eaa6c5197.