[ci skip] Remove link_to_function and button_from_function from guides

These methods were removed in cb9f7f4 and are no longer methods in the
Rails codebase.

Author: eileencodes

guides/source/action_view_overview.md

@@ -1420,18 +1420,6 @@ date_field_tag "dob"
 
 Provides functionality for working with JavaScript in your views.
 
-#### button_to_function
-
-Returns a button that'll trigger a JavaScript function using the onclick handler. Examples:
-
-```ruby
-button_to_function "Greeting", "alert('Hello world!')"
-button_to_function "Delete", "if (confirm('Really?')) do_delete()"
-button_to_function "Details" do |page|
-  page[:details].visual_effect :toggle_slide
-end
-```
-
 #### define_javascript_functions
 
 Includes the Action Pack JavaScript libraries inside a single `script` tag.
@@ -1456,15 +1444,6 @@ alert('All is good')
 </script>
 ```
 
-#### link_to_function
-
-Returns a link that will trigger a JavaScript function using the onclick handler and return false after the fact.
-
-```ruby
-link_to_function "Greeting", "alert('Hello world!')"
-# => <a onclick="alert('Hello world!'); return false;" href="#">Greeting</a>
-```
-
 ### NumberHelper
 
 Provides methods for converting numbers into formatted strings. Methods are provided for phone numbers, currency, percentage, precision, positional notation, and file size.