`ConsTuples`: remove `DoubleEndedIterator` implementation #706

Job	Run time
check format	7s
msrv	39s
doc	8s
check	8s
check (--no-default-features)	5s
test	52s
check (--no-default-features --features use_alloc)	6s
check (--all-targets --all-features)	17s
All checks succeeded	1s
	2m 23s

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