Remove deprecated get_magic_quotes* function call from setup.php

The two DAViCal functions

• check_magic_quotes_gpc (setup.php#153)
• check_magic_quotes_runtime (setup.php#157)

contain calls to PHP functions get_magic_quotes_gpc and get_magic_quotes_runtime which have been deprecated as of PHP 7.4.0. This should be taken into account in order to make the code up to date for PHP 7.4.0+.