Revert "python: use vendored tomli"

Now that Ubuntu 20.04 is not included anymore, there is no need to ship
it as part of QEMU; Ubuntu 22.04 includes it and Leap users anyway
need to install all the required dependencies from PyPI.

This mostly reverts commit ec77ee7634de123b7c899739711000fd21dab68b,
with just some changes to the wording.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

python/scripts/vendor.py

@@ -43,9 +43,6 @@ def main() -> int:
     packages = {
         "meson==1.2.3":
         "4533a43c34548edd1f63a276a42690fce15bde9409bcf20c4b8fa3d7e4d7cac1",
-
-        "tomli==2.0.1":
-        "939de3e7a6161af0c887ef91b7d41a53e7c5a1ca976325f429cb46ea9bc30ecc",
     }
 
     vendor_dir = Path(__file__, "..", "..", "wheels").resolve()