DOC-3234: remove incorrect placed upgrading link in nav.adoc.

Author: kemister85

modules/ROOT/nav.adoc

@@ -53,7 +53,6 @@
 **** xref:dotnet-projects.adoc[.NET projects]
 **** xref:bower-projects.adoc[Bower projects]
 **** xref:zip-install.adoc[{productname} .zip deployments]
-*** xref:upgrading.adoc[General upgrade information]
 * xref:how-to-guides.adoc[How-to guides]
 ** Learn the basics
 *** xref:basic-setup.adoc[Basic setup]