Remove suggestions from Elixir's Lasagna (#2273)

The function naming, regular expression and String suggestions aren't
applicable to the exercise anyway.

tracks/elixir/exercises/lasagna/mentoring.md

@@ -17,31 +17,3 @@ defmodule Lasagna do
   def alarm, do: "Ding!"
 end
 ```
-
-## Common suggestions
-
-
-If a solution uses names like `is_cooked` and `is_ready`,
-it can be pointed out that Elixir has the following naming convention:
-- `is_foo` should only be used for macros that can be used in guard clauses,
-- `foo?` should be used otherwise.
-
-Sources:
-- https://github.com/rrrene/elixir-style-guide#predicates
-- https://github.com/christopheradams/elixir_style_guide#predicate-macro-names-with-guards
-- https://github.com/lexmag/elixir-style-guide#predicate-funs-name
-
-### Usage of regular expressions
-
-This exercise can be solved without regular expressions and a student could be encouraged to try to do that.
- - Regular expressions are not known for their readability. `String.ends_with?(input, "?")` is more obvious than `Regex.match?(~r/\?$/, input)`.
- - It is a good habit to use simple tools for simple problems and advanced tools for advanced problems.
- - Elixir developers should be familiar with the `String` module and the functions it offers.
-
-### Hint functions for the truly stuck
-
-- [`String#trim/1`](https://hexdocs.pm/elixir/String.html#trim/1)
-- [`String#ends_with?/2`](https://hexdocs.pm/elixir/String.html#ends_with?/2)
-- [`String#downcase/2`](https://hexdocs.pm/elixir/String.html#downcase/2)
-- [`String#upcase/2`](https://hexdocs.pm/elixir/String.html#upcase/2)
-- `String.upcase(input) != String.downcase(input)` if there is a letter present.