Updating versioneer again, properly.

First time around we were using `versioneer install --no-vendor`, and
neglecting to remove the `versioneer.py` file from the toplevel, which
is still required by BuildStream's setup.py for a few reasons.

Instead, go back to `versioneer install --vendor` and update versioneer
files correctly.

Fixes #1855

Author: gtristan

pyproject.toml

@@ -20,8 +20,6 @@ requires = [
     # Require a new enough cython for the python versions we support
     "Cython>=0.29.25",
     "packaging",
-    # Versioneer is a build time dependency
-    "versioneer[toml]",
 ]
 build-backend = "setuptools.build_meta"