chore: remove redundant PHPStan baseline cleanup

[datamweb]

Description
Currently, the script uses bash -c to run rm and touch commands. While this works for many developers on Windows who have configured Git Bash in their system's PATH, it creates an implicit dependency. New contributors or those with a different setup may encounter errors, creating a barrier to entry.

It has been identified that the split-phpstan-baseline command (provided by shipmonk/phpstan-baseline-per-identifier) already incorporates its own logic to deleteOrphanedFiles as part of its process. This means the explicit cleanup step performed before split-phpstan-baseline is unnecessary and duplicative.

https://github.com/shipmonk-rnd/phpstan-baseline-per-identifier/blame/b997803a60f1f604b9fe0aed5d6d1edead010190/src/BaselineSplitter.php#L240-L274

See : #9865 (comment)

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

It's possible we no longer need manual cleanup of the .neon files. Please check it on your local machine.
See: #9865 (comment)

[datamweb]

@michalsn, thank you for your sharp eye and guidance.

[michalsn]

Thank you @datamweb