remove hook that may confuse and create difficulties

Author: rajumsys

docs/hooks.md

@@ -18,7 +18,7 @@ Hook names are prefixed with `wpsp_`.
 | wpsp_open_tracking           | Filter   |   
 | wpsp_click_tracking          | Filter   |
 | wpsp_template_id             | Filter   |  Use a different template ID
-| wpsp_substitution_content_tag_name| Filter   |  Use a different tag for content substitution. By default you needed to use `content` tag
+| wpsp_substitution_content_tag_name| Filter   |  Use a different tag for content substitution. By default you needed to use `content` tag. **IMPORTANT: DO NOT USE IT. IT'LL BE REMOVED IN NEXT RELEASE** 
 | wpsp_sender_email            | Filter   |
 | wpsp_sender_name             | Filter   |
 | wpsp_response_body           | Filter   |
@@ -27,4 +27,4 @@ Hook names are prefixed with `wpsp_`.
 | wpsp_reply_to                | Filter   |
 | wpsp_body_headers            | Filter   |   
 | wpsp_smtp_msys_api           | Filter   |
-| wpsp_transactional           | Filter   | Set whether an email is transactional or not. 
+| wpsp_transactional           | Filter   | Set whether an email is transactional or not.

mailer.http.class.php

@@ -92,8 +92,7 @@ protected function get_request_body()
             $body['content']['template_id'] = apply_filters('wpsp_template_id', $this->settings['template']);
 
             // supply substitution data so users can add variables to templates
-            $content_substitution_tag_name = apply_filters('wpsp_substitution_content_tag_name', 'content');
-            $body['substitution_data'][$content_substitution_tag_name] = $this->Body;
+            $body['substitution_data']['content'] = $this->Body;
             $body['substitution_data']['subject'] = $this->Subject;
             $body['substitution_data']['from_name'] = $sender['name'];
             $body['substitution_data']['from'] = $sender['name'] . ' <' . $sender['email'] . '>';