chore: deduplicate zero-collection test

[Olexandr88]

Removed test case for collecting zero tokens.

[RembrandtK]

Thanks for the cleanup effort! However, these two tests aren't actually duplicates — they cover different scenarios:

• The one at line 636 runs inside a parameterized loop with delegation and varied fee/tax configurations (4 combinations).
• The one at line 772 (removed here) runs with default parameters and no delegation.

Since they exercise different code paths through the rebate and fee distribution logic, I think we should keep both. Closing in favour of keeping the existing coverage.