Use specific term "image" in error UI, not "attachment" (#2592)

The new message for the crop feature, "The attachment could not be edited.", turned out to be awkward in some languages (French) where according to the translator it would be better to more specifically say "The image could not be edited." (as currently we can only edit images). Patch replaces error_media_edit_failed with a error_image_edit_failed and deletes the existing error_media_edit_failed-s.

app/src/main/res/values-zh-rCN/strings.xml

@@ -544,6 +544,5 @@
     <string name="tips_push_notification_migration">重新登录所有账户来启用推送通知支持。</string>
     <string name="dialog_push_notification_migration">为了通过 UnifiedPush 使用推送通知，Tusky 需要订阅你 Mastodon 服务器通知的权限。这需要重新登录来更改授予 Tusky 的 OAuth 作用域。使用此处或账户首选项中“重新登录”选项将保留你所有的本地草稿和缓存。</string>
     <string name="status_count_one_plus">1+</string>
-    <string name="error_media_edit_failed">无法编辑附件。</string>
     <string name="action_edit_image">编辑图片</string>
 </resources>