remove deprecation warning

Author: rmorshea

src/idom/config.py

@@ -5,7 +5,6 @@
 
 from pathlib import Path
 from tempfile import TemporaryDirectory
-from warnings import warn
 
 from ._option import Option as _Option
 
@@ -69,14 +68,3 @@
 
 For more information on changes to this feature flag see: https://github.com/idom-team/idom/issues/351
 """
-
-if not IDOM_FEATURE_INDEX_AS_DEFAULT_KEY.current:
-    warn(
-        "In the next release, the feature flag IDOM_FEATURE_INDEX_AS_DEFAULT_KEY will "
-        "be activated by default. To try this out before the next release simply set "
-        "IDOM_FEATURE_INDEX_AS_DEFAULT_KEY=1 as an environment variable. After this "
-        "change, you can revert to the old behavior by setting it to 0 instead. If you "
-        "have questions or issues with this change report them here: "
-        "https://github.com/idom-team/idom/issues/351",
-        DeprecationWarning,
-    )