Revert "rcu: add debug_rcu_head_queue"

This reverts commit b586bd847a0a705e9adba9d0ed31d665d7bc2d05.
Revert "rcu:demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status"

This reverts commit 46ac35759a20a6bcacc7c742a6d0823cf2565ea1.