add `std` feature to newly added dependency in contracts pallet (#5801)

* remove unnecessary re-export

* enable unleash

* Revert "enable unleash"

This reverts commit 30f11d7b.

* Revert "remove unnecessary re-export"

This reverts commit 74229f99.

* fix missing std def

* Revert "Revert "enable unleash""

This reverts commit 323fb913.

* Revert "Revert "Revert "enable unleash"""

This reverts commit 3f199674.