Deprecate unused `\OCP\Response::sendFile`

This function is unused in our own code and can be better achieved using the AppFramework. Also very easy to do grave mistaked using this function.

lib/private/response.php

@@ -214,6 +214,7 @@ class OC_Response {
 	/**
 	 * Send file as response, checking and setting caching headers
 	 * @param string $filepath of file to send
+	 * @deprecated Use \OCP\AppFramework\Http\StreamResponse or another AppFramework controller instead
 	 */
 	static public function sendFile($filepath) {
 		$fp = fopen($filepath, 'rb');

lib/public/response.php

@@ -37,6 +37,7 @@ namespace OCP;
 /**
  * This class provides convenient functions to send the correct http response headers
  * @since 4.0.0
+ * @deprecated Use AppFramework controllers instead and modify the response object
  */
 class Response {
 	/**
@@ -103,6 +104,7 @@ class Response {
 	 * Send file as response, checking and setting caching headers
 	 * @param string $filepath of file to send
 	 * @since 4.0.0
+	 * @deprecated Use \OCP\AppFramework\Http\StreamResponse or another AppFramework controller instead
 	 */
 	static public function sendFile( $filepath ) {
 		\OC_Response::sendFile( $filepath );