Remove EfficientDiD clustered SE fix claim from v2.7.5 CHANGELOG

The clustered SE formula fix shipped in PR #230 (v2.7.4). The remaining
stale-indices issue is still tracked in TODO.md and not fixed in this release.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: igerber

CHANGELOG.md

@@ -30,7 +30,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix CallawaySantAnna reg+cov control IF normalization and survey df calculation
 - Fix TripleDifference TSL double-weighting and RA nuisance linearization with survey weights
 - Fix ContinuousDiD bread normalization, fweight TSL scaling, and weighted-mass IF linearization
-- Fix EfficientDiD clustered SE formula in Hausman pretest
 - Fix BaconDecomposition exact-weight survey unit_share and empty-cell guard
 - Fix SunAbraham survey weight floor in overall ATT aggregation
 - Fix plotly event study for non-numeric periods, heatmap masking, color parser