chore: remove old deprecations

[tlambert03]

removes:

• _util.get_reader
• read_using_sdk argument to ND2File and imread
• unnest argument to unstructured_metadata()
• recorded_data property (is now events())

[codecov[bot]]

Codecov Report

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

Comparison is base (dfcc558) 95.51% compared to head (74d7935) 95.49%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #209 +/- ## ========================================== - Coverage 95.51% 95.49% -0.02% ========================================== Files 17 17 Lines 2317 2308 -9 ========================================== - Hits 2213 2204 -9 Misses 104 104 ```

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[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #209 will not alter performance

_{Comparing drop-deprecations (74d7935) with main (dfcc558)}

Summary

✅ 13 untouched benchmarks