Remove Ion.egg-info and build_sources.sh

[krishnans2006]

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Proposed changes

• Remove Ion.egg-info
• Make build_sources.sh obsolete, and remove any references to it in other scripts and CI

Brief description of rationale

Python eggs are no longer supported: they have been entirely replaced by wheels (see here, here, and here). Therefore, carrying around an Ion.egg-info and having to build sources is highly unnecessary.

Below is a (truncated) successful installation of intranet as a pip package, without Ion.egg-info:

Processing ./intranet
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Preparing metadata (pyproject.toml) ... done
...
Building wheels for collected packages: Ion
  Building wheel for Ion (pyproject.toml) ... done
  Created wheel for Ion: filename=Ion-1.0-py3-none-any.whl size=18169480 sha256=699a7c9abe22951aa166a4e5daf474e089d7be38dee907de9433a31cae94eecb
  Stored in directory: /home/krishnan/.cache/pip/wheels/7e/80/92/06ba346fc4361cb005b13fc798756c7e861000bc5219cbecc5
Successfully built Ion
Installing collected packages: ...
Successfully installed ...

This change is made possible by #1648.