Remove code related to the rails test command

Remove the mention about this command in the rails command's help
message and remove the "t" alias related to it.

railties/lib/rails/commands.rb

@@ -5,7 +5,6 @@
   "d"  => "destroy",
   "c"  => "console",
   "s"  => "server",
-  "t"  => "test",
   "db" => "dbconsole",
   "r"  => "runner"
 }
@@ -17,7 +16,6 @@
  generate    Generate new code (short-cut alias: "g")
  console     Start the Rails console (short-cut alias: "c")
  server      Start the Rails server (short-cut alias: "s")
- test        Running the test file (short-cut alias: "t")
  dbconsole   Start a console for the database specified in config/database.yml
              (short-cut alias: "db")
  new         Create a new Rails application. "rails new my_app" creates a