Remove shallow renderer from website navigation (#2785)

We still support it (and you can find this page in search), but we're transitioning away to community maintenance.
So we're deemphasizing it on the website.

Author: gaearon

content/docs/nav.yml

@@ -100,8 +100,6 @@
       title: SyntheticEvent
     - id: test-utils
       title: Test Utilities
-    - id: shallow-renderer
-      title: Shallow Renderer
     - id: test-renderer
       title: Test Renderer
     - id: javascript-environment-requirements
@@ -175,4 +173,4 @@
     - id: faq-versioning
       title: Versioning Policy
     - id: faq-internals
-      title: Virtual DOM and Internals
+      title: Virtual DOM and Internals