chore(AlgebraicGeometry): clean up erw and porting notes

[Vierkantor]

I searched for erw and porting note and did my best to fix them. One recurring issue is that ext got less powerful than in Lean 3, the best solution is probably to make more @[ext] lemmas. But that would require more thought about library design than I have available right now.

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[github-actions]

PR summary c2c78bae5d

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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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/declarations_diff.sh <optional_commit>

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

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

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Decrease in tech debt: (relative, absolute) = (20.56, 0.02)

Current number	Change	Type
3296	-22	porting notes
1283	-20	erw

Current commit c2c78bae5d
Reference commit 6d33eaf659

You can run this locally as

./scripts/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).