Remove AlwaysFailOperation
AlwaysFailOperation guards the case when we do not have a schema
context, which is exceeding rare and there is exactly one place
where we can check for null to detect non-presence of an operation.
Remove this implementation along with
NonApplyDelegatedModificationApplyOperation, making
MinMaxElementsValidation the only delegating implementation.
JIRA: YANGTOOLS-955
Change-Id: Id70814eced80dd80948a1a5601287977fa77cf12
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>