Fixed email subject field not being disabled if mailgun is not configured

no issue

- changed `disabled=deliveredAction` to `disabled=mailgunError` so that it's switching on the correct property
- removed all references to the unused `deliveredAction` property

ghost/admin/app/components/gh-publishmenu.js

@@ -16,7 +16,6 @@ export default Component.extend({
     saveTask: null,
     runningText: null,
     backgroundTask: null,
-    deliveredAction: null,
 
     _publishedAtBlogTZ: null,
     _previousStatus: null,

ghost/admin/app/templates/components/gh-post-settings-menu/email.hbs

@@ -32,7 +32,7 @@
                     input=(action (mut emailSubjectScratch) value="target.value")
                     focus-out=(action "setEmailSubject" emailSubjectScratch)
                     stopEnterKeyDownPropagation=true
-                    disabled=deliveredAction
+                    disabled=mailgunError
                     data-test-field="email-subject"}}
                 {{gh-error-message errors=post.errors property="emailSubject" data-test-error="email-subject"}}
             {{/gh-form-group}}

ghost/admin/app/templates/components/gh-publishmenu.hbs

@@ -9,8 +9,7 @@
             post=post
             saveType=saveType
             setSaveType=(action "setSaveType")
-            backgroundTask=this.backgroundTask
-            deliveredAction=this.deliveredAction}}
+            backgroundTask=this.backgroundTask}}
 
         {{else if (eq displayState "scheduled")}}
         {{gh-publishmenu-scheduled
@@ -26,7 +25,6 @@
             saveType=saveType
             setSaveType=(action "setSaveType")
             backgroundTask=this.backgroundTask
-            deliveredAction=this.deliveredAction
             memberCount=this.memberCount
             sendEmailWhenPublished=this.sendEmailWhenPublishedScratch}}
         {{/if}}

ghost/admin/app/templates/editor.hbs

@@ -59,7 +59,6 @@
                             setSaveType=(action "setSaveType")
                             onOpen=(action "cancelAutosave")
                             backgroundTask=this.backgroundLoader
-                            deliveredAction=this.deliveredAction
                             memberCount=this.memberCount}}
                     {{/if}}
                 {{/unless}}
@@ -135,7 +134,6 @@
             deletePost=(action "toggleDeletePostModal")
             updateSlug=updateSlug
             savePost=savePost
-            deliveredAction=this.deliveredAction
         }}
     {{/liquid-wormhole}}
 {{/if}}