replace KJ_ASSERT with LASSERT

inadvertently reintroduced KJ_ASSERT with recent refactor.
It uses __FILE__ which contains path to source, which is
fixed with LASSERT

src/http.cpp

@@ -268,8 +268,8 @@ Http::Http(Laminar &li) :
 
 Http::~Http()
 {
-    KJ_ASSERT(logWatchers.size() == 0);
-    KJ_ASSERT(eventPeers.size() == 0);
+    LASSERT(logWatchers.size() == 0);
+    LASSERT(eventPeers.size() == 0);
 }
 
 kj::Promise<void> Http::startServer(kj::Timer& timer, kj::Own<kj::ConnectionReceiver>&& listener)