Change show_side_navs: true|false to nav: both|none.

PiperOrigin-RevId: 233141605

Author: tensorflower-gardener

site/en/install/_index.yaml

@@ -4,7 +4,7 @@ description: <!--no description-->
 landing_page:
   body_class: tfo-install
   custom_css_path: /site-assets/css/style.css
-  show_side_navs: True
+  nav: both
   rows:
   - classname:
       devsite-landing-row-large-headings

site/en/tutorials/_index.yaml

@@ -4,7 +4,7 @@ description: <!--no description-->
 landing_page:
   body_class: tfo-tutorials
   custom_css_path: /site-assets/css/style.css
-  show_side_navs: true
+  nav: both
   rows:
   - heading: Get Started with TensorFlow
     description: >