exampleSite: Remove custom tag page demo

Fix #594 - error was caused by case mismatch between case of tag in
content front matter and case of tag in name of custom tag page folder.

Rather than rename the tag folder from 'academic' to 'Academic' to match
the tag case in the content front matter, let's just delete it for now.

Close #594

exampleSite/content/tags/academic/_index.md

@@ -1,14 +0,0 @@
-+++
-title = "Content tagged as 'Academic'"
-date = 2017-01-01T00:00:00
-math = false
-highlight = false
-
-# Optional featured image (relative to `static/img/` folder).
-[header]
-image = "headers/bubbles-wide.jpg"
-caption = ""
-
-+++
-
-Here is a list of all the content that has been tagged as *academic*.