Remove broken link (#1767)

The `examples` directory was removed with https://github.com/gohugoio/hugo/pull/9615.

content/en/troubleshooting/build-performance.md

@@ -4,7 +4,6 @@ linktitle: Build Performance
 description: An overview of features used for diagnosing and improving performance issues in site builds.
 date: 2017-03-12
 publishdate: 2017-03-12
-lastmod: 2017-03-12
 keywords: [performance, build]
 categories: [troubleshooting]
 menu:
@@ -16,10 +15,6 @@ aliases: []
 toc: true
 ---
 
-{{% note %}}
-The example site used below is from https://github.com/gohugoio/hugo/tree/master/examples/blog
-{{% /note %}}
-
 ## Template Metrics
 
 Hugo is a very fast static site generator, but it is possible to write