Prevent PYTHONHOME, set by Python_jll, from leaking in the Julia environment.

[maleadt]

It breaks loading Python from Julia, as done by e.g. Conda.jl.

$ jl --bug-report=rr-local 

julia> run(`python -c "import sys; print(sys.version)"`)
Python path configuration:
  PYTHONHOME = '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07'
  PYTHONPATH = (not set)
  program name = 'python'
  isolated = 0
  environment = 1
  user site = 1
  import site = 1
  sys._base_executable = '/usr/bin/python'
  sys.base_prefix = '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07'
  sys.base_exec_prefix = '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07'
  sys.platlibdir = 'lib'
  sys.executable = '/usr/bin/python'
  sys.prefix = '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07'
  sys.exec_prefix = '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07'
  sys.path = [
    '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07/lib/python310.zip',
    '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07/lib/python3.10',
    '/home/tim/Julia/depot/artifacts/7feba47da7f679e59da788f7b564290573ea4e07/lib/python3.10/lib-dynload',
  ]
Fatal Python error: init_fs_encoding: failed to get the Python codec of the filesystem encoding
Python runtime state: core initialized
ModuleNotFoundError: No module named 'encodings'