Functions::deleteFunction() doesn't check Runkit::isAvailable()

[stevegrunwell]

Before attempting to call runkit functions, we first need to make sure that runkit/runkit7 are installed and active; if not, we mark the current test as skipped:

use AssertWell\PHPUnitGlobalState\Support\Runkit;

if (! Runkit::isAvailable()) {
  $this->markTestSkipped('someMethod() requires Runkit be available, skipping.');
}

This check isn't happening in AssertWell\PHPUnitGlobalState\Functions::deleteFunction(), which can cause tests to error inappropriately if runkit isn't available.