Remove redundant CDP v8 shutdown

https://github.com/lightpanda-io/browser/pull/1614 improved our shutdown
behavior so that microtasks associated with a context wouldn't fire after the
context was disposed of. This involved having context-specific microtasks,
pumping the message loop, and prevent re-entry.

The shutdown code in CDP already had much of this behavior built-in, but it has
now become redundant. Most importantly the CDP shutdown logic did not prevent
re-entry.

Removing this code fixes a flaky WPT crash. I didn't seem to be tied to a
specific test, but rather a cross-context/page use-after-free that was saw
prior to 1614. I could reproduce it reliably by running `/wasm/core/`.

I'll be honest, it isn't clear to me why _removing_ the CDP cleanup helps.
Running the message loop and microtask _before_ our normal shutdown might be
unnecessary, but why would it crash? I don't know, but the CDP path is slightly
different in that it also involves Inspector shutdown. So there's still
something about this flow I don't quite understand. And, at least for this case
the current flow seems "correct".

src/cdp/cdp.zig

@@ -438,15 +438,10 @@ pub fn BrowserContext(comptime CDP_T: type) type {
             const browser = &self.cdp.browser;
             const env = &browser.env;
 
-            // Drain microtasks makes sure we don't have inspector's callback
-            // in progress before deinit.
-            env.runMicrotasks();
-
             // resetContextGroup detach the inspector from all contexts.
-            // It append async tasks, so we make sure we run the message loop
+            // It appends async tasks, so we make sure we run the message loop
             // before deinit it.
             env.inspector.?.resetContextGroup();
-            _ = env.pumpMessageLoop();
             env.inspector.?.stopSession();
 
             // abort all intercepted requests before closing the sesion/page