[2.0] Drop Python 2.7 support and pydevd-pycharm

The python helper image is a monolithic image that includes debugging support for all supported versions of Python. Maintaining older versions becomes a drag on space. For 2.0, we should:

- Drop Python 2.7 support: Python 2.7 was EOL January 1, 2020, and the [only service supporting Python 2.7 on Google Cloud](https://cloud.google.com/python/docs/python2-sunset) is App Engine, which doesn't use these debugging helpers.
- Drop `pydevd-pycharm`: it was added to support Cloud Code for IntelliJ, but they were unable to get it to work, whereas pydevd worked fine.

Users requiring Python 2.7 support can use Skaffold's `debug-helpers-registry` config setting to point to the v1 debug images (`gcr.io/k8s-skaffold/skaffold-debug-support/v1`) their own images.

El issue no indica archivos ni pruebas. Empieza por localizar la configuración de compilación de helper-image y las referencias a Python 2.7 y pydevd-pycharm; verifica cómo se ensamblan las imágenes v1 y 2.0. Se considera terminado cuando la imagen 2.0 ya no incluye ninguno de los dos componentes, mientras que la configuración documentada de v1 sigue disponible para los usuarios que necesiten Python 2.7.

Escrito por el modelo de indexación a partir del texto del issue.