migrate pallet-nft-fractionalization to benchmarking v2 syntax (#6301)

Migrates pallet-nft-fractionalization to benchmarking v2 syntax.

Part of:
* #6202

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Co-authored-by: Giuseppe Re <giuseppe.re@parity.io>
Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Bastian Köcher <git@kchr.de>