Don't use soft-deprecated for form_tag and form_for in the guides

Just tell people they exists and are discouraged in favor of `form_with`,
but they can still find them in some codebases, and people can still
and forever will be able to use it.

Author: rafaelfranca

guides/source/form_helpers.md

@@ -1338,4 +1338,4 @@ Generally, these helpers have the same name as their form builder counterparts p
 Using `form_tag` and `form_for`
 -------------------------------
 
-Before `form_with` was introduced in Rails 5.1 its functionality was split between [`form_tag`](https://api.rubyonrails.org/v5.2/classes/ActionView/Helpers/FormTagHelper.html#method-i-form_tag) and [`form_for`](https://api.rubyonrails.org/v5.2/classes/ActionView/Helpers/FormHelper.html#method-i-form_for). Both are now soft-deprecated in favor of `form_with`.
+Before `form_with` was introduced in Rails 5.1 its functionality was split between [`form_tag`](https://api.rubyonrails.org/v5.2/classes/ActionView/Helpers/FormTagHelper.html#method-i-form_tag) and [`form_for`](https://api.rubyonrails.org/v5.2/classes/ActionView/Helpers/FormHelper.html#method-i-form_for). Both are now discouraged in favor of `form_with`, but you can still find being used in some codebases.