chore: unexpose public sections with no defs

[felixpernegger]

This PR remove @[expose] from public sections when there are no (irredcible_)def's inside the section anyways, so there is no reason to expose the section (does not make a difference).

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[github-actions]

PR summary 676f0a2078

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 676f0a2).

• +0 new declarations
• −0 removed declarations

No declaration differences.

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No changes to strong technical debt.

Decrease in weak tech debt: (relative, absolute) = (147.00, 0.03)

Current number	Change	Type (weak)
4860	-147	exposed public sections

Current commit 676f0a2078
Reference commit a33a5ccd63

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).

[themathqueen]

I don't think there's consensus on whether we should make things @[expose] public section or not (regardless whether there may be definitions or not). I think it's just author's choice for now?

[felixpernegger]

I don't think there's consensus on whether we should make things @[expose] public section or not (regardless whether there may be definitions or not). I think it's just author's choice for now?

I thought its discouraged since its tracked as weak tech debt?

[grunweg]

I don't think there's consensus on whether we should make things @[expose] public section or not (regardless whether there may be definitions or not). I think it's just author's choice for now?

For files with definitions, I agree it's author's choice. I'm not so convinced for files without definitions...
but then files without definitions may gain some in the future. Hm.

[themathqueen]

To be fair, most files with @[expose] public section were added when we transferred to the module system. So the authors didn't really have a say in it

So, I guess removing them is just as fair play? Maybe?

[felixpernegger]

I guess the larger issue at hand why we have so many exposed public sections, is because in 95% of definitions in math you want to know whats underneath.