pallet-treasury: Improve `remove_approval` benchmark

[bkchr]

When SpendOrigin doesn't return any succesful_origin, it doesn't mean that RejectOrigin will do the same. Thus, this pr fixes a potential wrong benchmarked weight for when SpendOrigin is set to e.g. NeverOrigin.

[paritytech-cmd-bot-polkadot-sdk[bot]]

Created backport PR for stable2407:

• 5739 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-5713-to-stable2407
git worktree add --checkout .worktree/backport-5713-to-stable2407 backport-5713-to-stable2407
cd .worktree/backport-5713-to-stable2407
git reset --hard HEAD^
git cherry-pick -x 9cdbdc5a73f3c2d1d9afdf266799f249c3c04c2d
git push --force-with-lease

[paritytech-cmd-bot-polkadot-sdk[bot]]

Successfully created backport PR for stable2409:

• 5740