[MM-63774] Allow users to leave private channels when there is only 1 member (#30746)

* allow last user to leave private channel
---------
Co-authored-by: Mattermost Build <build@mattermost.com>

server/i18n/en.json

@@ -419,10 +419,6 @@
     "id": "api.channel.leave.direct.app_error",
     "translation": "Unable to leave a direct message channel."
   },
-  {
-    "id": "api.channel.leave.last_member.app_error",
-    "translation": "You're the only member left, try removing the Private Channel instead of leaving."
-  },
   {
     "id": "api.channel.leave.left",
     "translation": "%v left the channel."