If pip is included in the environment.yml file as a dependency, we should automatically drop it

[martinRenou]

Description

cc. @psychemedia

Specifying an environment containing pip may result in unwanted errors:

name: xeus-python-kernel
channels:
  - https://repo.mamba.pm/emscripten-forge
  - https://repo.mamba.pm/conda-forge
dependencies:
  - pip

We should take care of this case and drop pip from the list automatically.

[martinRenou]

After trying in #170 this seems to not be problematic actually. pip being a noarch package it can be installed in the environment. We may want to filter out pip in the packed environment though. See emscripten-forge/empack#83