[docs] Remove / adjusted auto-instr and distro pages since they've moved

[chalin]

• Contributes to
  • Non-API docs should be hosted on the website only #2172
  • Migrate Python docs to this repo opentelemetry.io#1109
• This PR is the Python-docs counterpart to [opentelemetry.io PR#1118](Python: add automatic instrumentation and distro pages opentelemetry.io#1118.
  • For the auto-instrumentation page, guide readers to the new page on the OTel website.
  • For the distro page, this is where it was moved to:
    https://opentelemetry-python.readthedocs.io/en/latest/examples/distro/README.html → https://opentelemetry.io/docs/instrumentation/python/distro/

/cc @cartermp @austinlparker