Remove PcntSource

[bugadani]

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Submission Checklist 📝

• I have updated existing examples or added new ones (if applicable).
• I have used cargo xtask fmt-packages command to ensure that all changed code is formatted correctly.
• My changes were added to the CHANGELOG.md in the proper section.
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Pull Request Details 📖

Description

These are no longer necessary, users can just configure a pin and pass it to PCNT.

[bjoernQ]

Works fine

[JurajSadel]

Thanks!