[Ref] Simplify is_email_receipt in sendMail

This function has evolved through refactoring so there was a time when this code needed to decide whether to
send emails out or not. However, the function is now called more deliberately -ie
1) from completeTransaction - where it is only called if the decision to send an email is made
2) from the search action send Email receipts - where a user has made the decision to send (or pdf)
receipts and unless it's being called with returnMessageText = TRUE (to construct a pdf) then
send makes sense

Ergo we should send unless returnMessageText = TRUE

CRM/Contribute/BAO/Contribution.php

@@ -2927,7 +2927,7 @@ public function composeMessageArray(&$input, &$ids, &$values, $returnMessageText
 
     //not really sure what params might be passed in but lets merge em into values
     $values = array_merge($this->_gatherMessageValues($input, $values, $ids), $values);
-    $values['is_email_receipt'] = $this->isEmailReceipt($input, $values);
+    $values['is_email_receipt'] = !$returnMessageText;
     if (!empty($input['receipt_date'])) {
       $values['receipt_date'] = $input['receipt_date'];
     }
@@ -5706,23 +5706,6 @@ protected function loadRelatedEntitiesByID($ids) {
     }
   }
 
-  /**
-   * Should an email receipt be sent for this contribution when complete.
-   *
-   * @param array $input
-   *
-   * @return mixed
-   */
-  protected function isEmailReceipt($input) {
-    if (isset($input['is_email_receipt'])) {
-      return $input['is_email_receipt'];
-    }
-    if (!empty($this->_relatedObjects['contribution_page_id'])) {
-      return $this->_relatedObjects['contribution_page_id']->is_email_receipt;
-    }
-    return TRUE;
-  }
-
   /**
    * Function to replace contribution tokens.
    *