flit_core bundles the 'tomli' TOML parser, to avoid a bootstrapping problem.
tomli is packaged using Flit, so there would be a dependency cycle when building
from source. Vendoring a copy of tomli avoids this. The code in tomli is under
the MIT license, and the LICENSE file is in the .dist-info folder.

If you want to unbundle tomli and rely on it as a separate package, you can
replace the package with Python code doing 'from tomli import *'. You will
probably need to work around the dependency cycle between flit_core and tomli.

Bundling a TOML parser should be a special case - I don't plan on bundling
anything else in flit_core (or depending on any other packages).
I hope that a TOML parser will be added to the Python standard library, and then
this bundled parser will go away.