style: omit <| before fun

[JovanGerb]

This PR replaces <| fun with fun as these are equivalent.

This was done directly with a single search and replace.

This is similar to #31769

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[github-actions]

PR summary 5db4c074f8

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 5db4c07).

• +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 5db4c074f8
Reference commit 80cbd0498a

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.py 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]

This is a little bit less trivial with regex, but while you are at it, maybe also replace
"foo (fun a \maps b) \n" with "foo fun a \maps b \n" ?

[JovanGerb]

That one is definitely harder to do automatically, because you can have

foo (fun a => ...)
  (fun b => ...)
  (fun c => ...)

Here you can only remove the brackets in the last line, but even then it might look better with keeping all brackets in place, because then the arguments line up better.

[JovanGerb]

I wonder if it would make sense to have a style linter for redundant uses of <|.