gh-38867: Fix duplicate install of config.py in meson build
The `configure_file` command creating this `config.py` file already has
`install: true` which makes it installed by default. Installing it again
here creates a duplicate entry in wheel packages, which breaks
installing them with some tools (eg. python-installer).
URL: https://github.com/sagemath/sage/pull/38867
Reported by: Antonio Rojas
Reviewer(s): Tobias Diez
