diff --git a/changelogs/fragments/1-cleanup.yml b/changelogs/fragments/1-cleanup.yml
new file mode 100644
index 0000000..73e989f
--- /dev/null
+++ b/changelogs/fragments/1-cleanup.yml
@@ -0,0 +1,4 @@
+minor_changes:
+  - "Remove unused code (https://github.com/ansible-community/antsibull-core/pull/1)."
+removed_features:
+  - "Remove package ``antsibull_core.utils.transformations`` (https://github.com/ansible-community/antsibull-core/pull/1)."
diff --git a/src/antsibull_core/logging.py b/src/antsibull_core/logging.py
index 858f4b0..9c94012 100644
--- a/src/antsibull_core/logging.py
+++ b/src/antsibull_core/logging.py
@@ -219,20 +219,6 @@ def run(args):
 mlog.debug('logging loaded')
 
 
-def plugin_filter():
-    """
-    Filter out messages which come from plugin error output.
-
-    :arg msg: A :twiggy:obj:`twiggy.message.Message` object which would be filtered
-    """
-    def wrapped(msg):
-        return (
-            msg.fields['func'] == 'write_plugin_rst' and
-            msg.fields['mod'] == 'antsibull.write_docs'
-        )
-    return wrapped
-
-
 def initialize_app_logging():
     """
     Change log settings to make sense for an application.
@@ -251,4 +237,4 @@ def initialize_app_logging():
     twiggy.quick_setup(min_level=_level)
 
 
-__all__ = ('log', 'initialize_app_logging', 'plugin_filter')
+__all__ = ('log', 'initialize_app_logging')
diff --git a/src/antsibull_core/utils/transformations.py b/src/antsibull_core/utils/transformations.py
deleted file mode 100644
index 6385e20..0000000
--- a/src/antsibull_core/utils/transformations.py
+++ /dev/null
@@ -1,23 +0,0 @@
-# coding: utf-8
-# Author: Felix Fontein <felix@fontein.de>
-# Author: Toshio Kuratomi <tkuratom@redhat.com>
-# License: GPLv3+
-# Copyright: Ansible Project, 2021
-"""General transformation functions."""
-
-import typing as t
-from collections import defaultdict
-
-
-def get_collection_namespaces(collection_names: t.Iterable[str]) -> t.Dict[str, t.List[str]]:
-    """
-    Return the plugins which are in each collection.
-
-    :arg collection_names: An iterable of collection names.
-    :returns: Mapping from collection namespaces to list of collection names.
-    """
-    namespaces = defaultdict(list)
-    for collection_name in collection_names:
-        namespace, name = collection_name.split('.', 1)
-        namespaces[namespace].append(name)
-    return namespaces