Use single db call

src/invidious/database/users.cr

@@ -50,10 +50,9 @@ module Invidious::Database::Users
   end
 
   def mark_watched(user : User, vid : String)
-    mark_unwatched(user, vid)
     request = <<-SQL
       UPDATE users
-      SET watched = array_append(watched, $1)
+      SET watched = array_append(array_remove(watched, $1), $1)
       WHERE email = $2
     SQL