sched: fair: Disable double lock/unlock balance in detach_task()

CONFIG_LOCK_STAT shows warnings in detach_task() for releasing a
pinned lock. The warnings are due to the calls to
double_unlock_balance() added to snapshot WALT. Lets disable them if
not building with SCHED_WALT.

Bug: 123720375
Change-Id: Ibfa28b1434fa6006fa0117fd2df1a3eadb321568
Signed-off-by: Miguel de Dios <migueldedios@google.com>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>