session: Destroy Warning

This addresses the `session_destroy()` warning many people are receiving
with PHP 7+. The warning states `PHP Warning:  session_destroy(): Session
callback expects true/false return value`. This is because our session
destroy method does not always return true/false, sometimes it returns
`int(1)`. This adds a check to see if the session was not deleted
successfully, if not it returns false, otherwise it returns true. This will
ensure `session_destroy()` always receives a true/false return value.