sched: delete unused & buggy function definitions

None of these functions does what its name implies when
CONFIG_SCHED_WALT=n. While all are currently unused, future patches
could introduce subtle bugs by calling any of them from non WALT
specific code. Delete the functions so it's obvious if new callers are
added.

Test: build kernel
Change-Id: Ib7552afb5668b48fe2ae56307016e98716e00e63
Signed-off-by: Connor O'Brien <connoro@google.com>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>