Coding Standards: Fix instances of WordPress.PHP.NoSilencedErrors.Discouraged.

Noteable changes:
- The `magic_quotes_runtime` and `magic_quotes_sybase` settings were removed in PHP 5.4, so no longer need to be set.
- Some functions that use external libraries can generate errors that can't be tested for, so are globally allowed to silence errors.
- Quite a few functions would cause errors if `safe_mode` was set. This setting was removed in PHP 5.4.
- Only a handful of `header()` calls needed corresponding `headers_sent()` checks for unit tests to pass, but more may need to be added as the nightlies builds are tested.

See #46732.


git-svn-id: https://develop.svn.wordpress.org/trunk@45611 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -1279,19 +1279,7 @@ class WP_REST_Server {
 	 * @param string $key Header key.
 	 */
 	public function remove_header( $key ) {
-		if ( function_exists( 'header_remove' ) ) {
-			// In PHP 5.3+ there is a way to remove an already set header.
-			header_remove( $key );
-		} else {
-			// In PHP 5.2, send an empty header, but only as a last resort to
-			// override a header already sent.
-			foreach ( headers_list() as $header ) {
-				if ( 0 === stripos( $header, "$key:" ) ) {
-					$this->send_header( $key, '' );
-					break;
-				}
-			}
-		}
+		header_remove( $key );
 	}
 
 	/**