About pio core override extensions.json enhancement

[seishinkouki]

• Feature Request.
  Start by telling us what problem you’re trying to solve. Often a solution
  already exists! Don’t send pull requests to implement new features without first getting our
  support. Sometimes we leave features out on purpose to keep the project small.

Currently, pio will keep user custom [recommendations] section when overriding extensions.json, I think it will be helpful keep both custom [recommendations] and [unwanted Recommendations] sections.

[ivankravets]

Please re-test with pio upgrade --dev.

[seishinkouki]

Please re-test with pio upgrade --dev.

it work as expected, thanks