Clean up ctor

Author: mrober

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/KeyValueBuilder.kt

@@ -16,14 +16,15 @@
 
 package com.google.firebase.crashlytics
 
-/** Helper class to enable fluent syntax in [setCustomKeys] */
-@Suppress("DEPRECATION")
-class KeyValueBuilder(
-  // TODO(mrober): Remove this param and make ctor internal in 2025.
-  @Deprecated(message = "The crashlytics instance is no longer needed and will be removed in 2025.")
-  private val crashlytics: FirebaseCrashlytics? = null
+/** Helper class to enable convenient syntax in [setCustomKeys] */
+class KeyValueBuilder private constructor(
+  private val crashlytics: FirebaseCrashlytics?,
+  private val builder: CustomKeysAndValues.Builder,
 ) {
-  private val builder = CustomKeysAndValues.Builder()
+  @Deprecated("Do not construct this directly. Use `setCustomKeys` instead. To be removed in 2025.")
+  constructor(crashlytics: FirebaseCrashlytics) : this(crashlytics, CustomKeysAndValues.Builder())
+
+  internal constructor() : this(crashlytics = null, CustomKeysAndValues.Builder())
 
   internal fun build(): CustomKeysAndValues = builder.build()