Remove unused translatable strings (#12643)

* Remove unused “salmon_url” string

* Remove more unused translatable strings

The following strings all used to be on the admin account page
but aren't used anymore: profile_url, outbox_url, followers_url, feed_url

config/locales/en_GB.yml

@@ -105,9 +105,7 @@ en_GB:
       email_status: Email status
       enable: Enable
       enabled: Enabled
-      feed_url: Feed URL
       followers: Followers
-      followers_url: Followers URL
       follows: Follows
       header: Header
       inbox_url: Inbox URL
@@ -134,10 +132,8 @@ en_GB:
       most_recent_ip: Most recent IP
       no_limits_imposed: No limits imposed
       not_subscribed: Not subscribed
-      outbox_url: Outbox URL
       pending: Pending review
       perform_full_suspension: Suspend
-      profile_url: Profile URL
       promote: Promote
       protocol: Protocol
       public: Public
@@ -159,7 +155,6 @@ en_GB:
         moderator: Moderator
         staff: Staff
         user: User
-      salmon_url: Salmon URL
       search: Search
       shared_inbox_url: Shared inbox URL
       show: