Revert "docs: Add www.bullion-investor.com to the showcase gallery"

No hugo generator tag, probably not a Hugo a site, certainly not a showcase.

This reverts commit b5bc74ca46.

docs/content/showcase/bullion-investor.md

@@ -1,22 +0,0 @@
----
-date: 2016-10-28T09:10:00+02:00
-description: "German language gold report. Tips, tricks, news & glossary on coins, bullion bars and precious-metals investments."
-sitelink: http://www.bullion-investor.com/report/
-tags:
-- 'gold price'
-- blog
-- coins
-- deutschland
-- finance
-- germany
-- gold
-- investment
-- news
-- numismatics
-- palladium
-- platinum
-- report
-- silver
-thumbnail: /img/bullion-investor-com.png
-title: GOLDREPORT — Gold, Silver & Numismatics News
----