[11.x] fix PHPDoc for \Illuminate\Database\Connection

[taka-oyama]

$events and $transactionsManager can both be set to null using unsetEventDispatcher() and unsetTransactionManager.

As for getElapsedTime($start), doc says int $start but if you look at how it's actually used, it's passing a float (see below).

framework/src/Illuminate/Database/Connection.php

Lines 789 to 791 in 5c9cb78

	$this->logQuery(
	$query, $bindings, $this->getElapsedTime($start)
	);