chore(AlgebraicGeometry/GammaSpecAdjunction): remove an erw

[yuanyi-350]

• rewrites toStalk_stalkMap_toΓSpec by folding the old erw into the surrounding simp only/rw chain

Extracted from #38415

[github-actions]

PR summary 5d69f04e65

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

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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

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

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

---

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

Current number	Change	Type
585	-1	erw

Current commit 5956170647
Reference commit 5d69f04e65

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).

[dagurtomas]

Let's keep the more robust rw, it's a bit hard to see what's happening inside the simp only, especially with Category.assoc in both directions:

  rw [PresheafedSpace.Hom.stalkMap,
    ← algebraMap_germ (basicOpen (1 : Γ.obj (op X))) _ (by rw [basicOpen_one]; trivial),
    ← Category.assoc, Category.assoc (CommRingCat.ofHom _), stalkFunctor_map_germ, ← Category.assoc,
    X.toΓSpecSheafedSpace_app_eq, X.toΓSpecCApp_spec, Γgerm,
    ← dsimp% stalkPushforward_germ _ _ X.presheaf ⊤]