Removed two imported functions - these are mocked in tests

We have to find a better method to test functionality which depends on
internal functions.

Author: michalbundyra

src/Response/SapiEmitterTrait.php

@@ -10,8 +10,6 @@
 use Psr\Http\Message\ResponseInterface;
 use RuntimeException;
 
-use function header;
-use function headers_sent;
 use function ob_get_length;
 use function ob_get_level;
 use function sprintf;