Move apt-system-requirements.txt into apt-list-dev-tools.txt

[mhucka]

Description of the issue

There is a file apt-system-requirements.txt at the top level of the Cirq repo. As far as I can find, the only place this file is referenced is in docs/dev/development.md, where the instructions say to do this:

cat apt-system-requirements.txt dev_tools/conf/apt-list-dev-tools.txt | xargs sudo apt-get install --yes

The file systems to have been introduced back in 2018. It looks like things may have been refactored and moved around since then. It's not obvious why there's a split between the two files (apt-system-requirements.txt and apt-list-dev-tools.txt), and so, I'd like to propose that we merge the content of apt-system-requirements.txt into apt-list-dev-tools.txt and get rid of the former file. The rationale is to simplify things a little bit and slightly reduce confusion.

Cirq version

1.5.0.dev