:fire: Remove Pipfile.lock from the repository (each contributor can keep his/her...

:fire: Remove Pipfile.lock from the repository (each contributor can keep his/her locally)

* :fire: Remove Pipfile.lock

Being a library, it should work independent of locking of dependency tree.

The Pipfile (and Pipfile.lock) is only used locally for development of FastAPI itself, it doesn't affect final users (that is controlled with pyproject.toml).

The Pipfile.lock adds unnecessary noise to PRs that update/upgrade development packages, and the locking is not the same in all environments (e.g. Linux, Mac, and Windows).

Each FastAPI contributor (developing FastAPI itself) can have his/her own Pipfile.lock, but it doesn't have to be in git.

* :see_no_evil: Add Pipfile.lock to .gitignore