[Merged by Bors] - chore(LinearAlgebra/Matrix/Block): remove an erw

[yuanyi-350]

• rewrites BlockTriangular.det to replace a simp only plus erw pair with a single rw
• uses Matrix.det_reindex_self he.symm directly in the rewrite chain

Extracted from #38415

[github-actions]

PR summary 9268b22206

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## summary with just the declaration names:
./scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

---

Decrease in tech debt: (relative, absolute) = (1.00, 0.00)

Current number	Change	Type
628	-1	erw

Current commit 4e55520c24
Reference commit 9268b22206

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[grunweg]

Thanks!
bors merge

[mathlib-bors]

Pull request successfully merged into master.

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