Use non-native token to benchmark xcm on asset hub (#7893)

Asset Hub was using the native token for benchmarking xcm instructions.
This is not the best since it's cheaper than using something in
`pallet-assets` for example.
Had to remove some restrictive checks from `pallet-xcm-benchmarks`.

I'll bring back the checks with a better framework in the future that
allows for handling multiple assets (`fungibles::*` traits).

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Co-authored-by: cmd[bot] <41898282+github-actions[bot]@users.noreply.github.com>