diff --git a/pom.xml b/pom.xml
index 56c802e7..a859574b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -252,6 +252,9 @@
                         <excludes>
                             <!-- public -->
                             <!-- removed -->
+                            <exclude>
+                                com.fasterxml.jackson.module.kotlin.KotlinModule#getEnabledSingletonSupport()
+                            </exclude>
                             <exclude>com.fasterxml.jackson.module.kotlin.MissingKotlinParameterException</exclude>
                             <!-- internal -->
                             <exclude>
diff --git a/release-notes/CREDITS-2.x b/release-notes/CREDITS-2.x
index 80485b08..92f2773d 100644
--- a/release-notes/CREDITS-2.x
+++ b/release-notes/CREDITS-2.x
@@ -18,6 +18,7 @@ Contributors:
 # 2.21.0 (not yet released)
 
 WrongWrong (@k163377)
+* #1043: Cleanup of deprecated contents
 * #1042: Remove old StrictNullChecks
 * #1041: Remove MissingKotlinParameterException
 * #1039: Update settings for 2.20
diff --git a/release-notes/VERSION-2.x b/release-notes/VERSION-2.x
index 168a2abe..8876b206 100644
--- a/release-notes/VERSION-2.x
+++ b/release-notes/VERSION-2.x
@@ -18,6 +18,7 @@ Co-maintainers:
 
 2.21.0 (not yet released)
 
+#1043: Deprecated content has been cleaned up with the version upgrade.
 #1042: The old StrictNullChecks backend has been removed.
   This improves the throughput of deserialization slightly.
 #1041: The deprecated MissingKotlinParameterException has been removed.
diff --git a/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinModule.kt b/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinModule.kt
index c36dca09..66946221 100644
--- a/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinModule.kt
+++ b/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinModule.kt
@@ -48,24 +48,6 @@ class KotlinModule private constructor(
     val useJavaDurationConversion: Boolean = UseJavaDurationConversion.enabledByDefault,
     newStrictNullChecks: Boolean = NewStrictNullChecks.enabledByDefault,
 ) : SimpleModule(KotlinModule::class.java.name, PackageVersion.VERSION) {
-    /*
-     * Prior to 2.18, an older Enum called SingletonSupport was used to manage feature.
-     * To deprecate it and replace it with singletonSupport: Boolean, the following steps are in progress.
-     *
-     * 1. add enabledSingletonSupport: Boolean property
-     * 2. delete SingletonSupport class and change the property to singletonSupport: Boolean
-     * 3. remove the enabledSingletonSupport property
-     *
-     * Now that 2 is complete, deprecation is in progress for 3.
-     */
-    @Deprecated(
-        level = DeprecationLevel.ERROR,
-        message = "This property is scheduled to be removed in 2.21 or later" +
-                " in order to unify the use of KotlinFeature.",
-        replaceWith = ReplaceWith("singletonSupport")
-    )
-    val enabledSingletonSupport: Boolean get() = singletonSupport
-
     // To reduce the amount of destructive changes, no properties will be added to the public.
     val strictNullChecks: Boolean = if (strictNullChecks) {
         if (newStrictNullChecks) {
diff --git a/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinSerializers.kt b/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinSerializers.kt
index 42aabc2f..94f9b7f2 100644
--- a/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinSerializers.kt
+++ b/src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinSerializers.kt
@@ -48,11 +48,7 @@ object ULongSerializer : StdSerializer<ULong>(ULong::class.java) {
     }
 }
 
-@Deprecated(
-    message = "This class was published by mistake. It will be removed in `2.22.0` as it is no longer used internally.",
-    level = DeprecationLevel.WARNING
-)
-object ValueClassUnboxSerializer : StdSerializer<Any>(Any::class.java) {
+internal object ValueClassUnboxSerializer : StdSerializer<Any>(Any::class.java) {
     private fun readResolve(): Any = ValueClassUnboxSerializer
 
     override fun serialize(value: Any, gen: JsonGenerator, provider: SerializerProvider) {