Use custom iree.dev domain in links to documentation site. (#15036)

Follow-up to https://github.com/openxla/iree/pull/15008 and some GitHub
configuration changes that switched us to using a custom domain for our
GitHub pages hosting.

Background:

* We acquired this domain for hosting https://perf.iree.dev/ years ago,
with some aspirations to use the domain for other pages eventually.
* We tried to use the domain with our GitHub Pages content at one point,
but ran into some issues that resulted in buggy redirects and
certificate errors. A few weeks ago we tried that again and succeeded.

Note that we had also considered using the `docs` subdomain, i.e.
`https://docs.iree.dev/`. That still seems tempting, but would require
more domain configuration work. Until we use a subdomain like that or
explore the workarounds in
https://github.com/orgs/community/discussions/23184, the `www` part of
URLs is required.
diff --git a/samples/colab/tensorflow_hub_import.ipynb b/samples/colab/tensorflow_hub_import.ipynb
index 36b67f1..7cc5801 100644
--- a/samples/colab/tensorflow_hub_import.ipynb
+++ b/samples/colab/tensorflow_hub_import.ipynb
@@ -58,7 +58,7 @@
         "\n",
         "At the end of the notebook, the compilation artifacts are compressed into a .zip file for you to download and use in an application.\n",
         "\n",
-        "See also https://openxla.github.io/iree/ml-frameworks/tensorflow/."
+        "See also https://iree.dev/guides/ml-frameworks/tensorflow/."
       ]
     },
     {
@@ -77,7 +77,7 @@
       },
       "source": [
         "%%capture\n",
-        "!python -m pip install iree-compiler iree-runtime iree-tools-tf -f https://openxla.github.io/iree/pip-release-links.html"
+        "!python -m pip install iree-compiler iree-runtime iree-tools-tf -f https://iree.dev/pip-release-links.html"
       ],
       "execution_count": 11,
       "outputs": []