chore: simplify show _ from by _ to show _ by _

[kbuzzard]

show X from t proves X using the term t; show X by tac proves X using the tactic tac.

show X from by tac is thus a redundant lengthening of show X by tac.

This replaces all 21 occurrences of show _ from by _ in the library with show _ by _.

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(Note: there are also 10 suffices _ from by _ occurrences -- should I change them in this PR too?)

[github-actions]

PR summary b331e6c19f

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 (regex)

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.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit b331e6c).

• +0 new declarations
• −0 removed declarations

No declaration differences.

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No changes to strong technical debt.

No changes to weak technical debt.

Current commit b331e6c19f
Reference commit ae588ec23e

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).

[felixpernegger]

A quick search that suffices foo from by also appears a couple of times, which culd also be shortened. (I didnt read the description fully...)

And I think you missed one occurence in Mathlib/Topology/Algebra/Monoid.lean (which goes over multiple lines, this is the only from by pattern doing that

[kbuzzard]

Thanks! I've added that change.

[grunweg]

I'll be happy to review the suffices change also, but that can also be a separate PR.

[grunweg]

The diff so far LGTM; is there a reason this PR is still labelled WIP?