DEV: remove targetUsernames deprecation

DEV: remove targetUsernames deprecation

Stable already has this rename, no need to carry the deprecation anymore.

diff --git a/app/assets/javascripts/discourse/models/composer.js b/app/assets/javascripts/discourse/models/composer.js
index 0f6d9ae..9c16503 100644
--- a/app/assets/javascripts/discourse/models/composer.js
+++ b/app/assets/javascripts/discourse/models/composer.js
@@ -77,8 +77,6 @@ const CLOSED = "closed",
     composerTime: "composerTime",
     typingTime: "typingTime",
     postId: "post.id",
-    // TODO remove together with 'targetUsername' deprecations
-    usernames: "targetUsernames",
     recipients: "targetRecipients"
   },
   _add_draft_fields = {},
@@ -343,14 +341,6 @@ const Composer = RestModel.extend({
   },
 
   @discourseComputed("targetRecipients")
-  targetUsernames(targetRecipients) {
-    deprecated(
-      "`targetUsernames` is deprecated, use `targetRecipients` instead."
-    );
-    return targetRecipients;
-  },
-
-  @discourseComputed("targetRecipients")
   targetRecipientsArray(targetRecipients) {
     const recipients = targetRecipients ? targetRecipients.split(",") : [];
     const groups = new Set(this.site.groups.map(g => g.name));

GitHub sha: 20d8b49a