Remove mention of --file-store from tracking docs (mlflow#1418)

Fixing based on feedback from mlflow slack

docs/source/tracking.rst

@@ -358,11 +358,7 @@ backend as ``./path_to_store`` or ``file:/path_to_store`` and a *database-backed
 `SQLAlchemy database URI <https://docs.sqlalchemy.org/en/latest/core/engines
 .html#database-urls>`_. The database URI typically takes the format ``<dialect>+<driver>://<username>:<password>@<host>:<port>/<database>``.
 MLflow supports the database dialects ``mysql``, ``mssql``, ``sqlite``, and ``postgresql``.
-Drivers are optional. If you do not specify a driver, SQLAlchemy uses a dialect's default driver.
-For backwards compatibility, ``--file-store`` is an alias for ``--backend-store-uri``. 
-For example, ``--backend-store-uri sqlite:///mlflow.db`` would create a local SQLite database.
-
-For backwards compatibility, ``--file-store`` is an alias for ``--backend-store-uri``.
+Drivers are optional. If you do not specify a driver, SQLAlchemy uses a dialect's default driver. For example, ``--backend-store-uri sqlite:///mlflow.db`` would use a local SQLite database.
 
 .. important::