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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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]

CodSpeed Performance Report

Merging #209 will not alter performance

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

Summary

✅ 13 untouched benchmarks