fix: don't remove while iterating

[kylezs]

Pull Request

Checklist

Please conduct a thorough self-review before opening the PR.

• [x] I am confident that the code works.
• [x] I have written sufficient tests.
• [x] I have written and tested required migrations.
• [x] I have updated documentation where appropriate.

Summary

The docs here: https://paritytech.github.io/polkadot-sdk/master/frame_support/storage/trait.IterableStorageMap.html#tymethod.iter_keys say you shouldn't remove when iterating, so even though it's probably ok, best not to.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 71%. Comparing base (a2fcb8f) to head (20e036f). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5460 +/- ## ====================================== - Coverage 72% 71% -0% ====================================== Files 494 494 Lines 87703 87580 -123 Branches 87703 87580 -123 ====================================== - Hits 62711 62532 -179 - Misses 22381 22435 +54 - Partials 2611 2613 +2 ```

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