Change robots.txt to exclude only media proxy URLs (#10038)

* Revert "Change robots.txt to exclude some URLs (#10037)"

This reverts commit 0e8ebc2371.

* Let's block media_proxy

/media_proxy/ is a dynamic route used for requesting uncached media, so it's
probably bad to let crawlers use it

* misleading comment

public/robots.txt

@@ -1,13 +1,4 @@
-User-Agent: *
+# See http://www.robotstxt.org/robotstxt.html for documentation on how to use the robots.txt file
-Disallow: /users/*/followers
+
-Disallow: /users/*/following
+User-agent: *
-Disallow: /@*/media
+Disallow: /media_proxy/
-Disallow: /@*/with_replies
-Disallow: /@*/tagged/*
-Disallow: /media_proxy/*
-Disallow: /emoji/*
-Disallow: /packs/*
-Disallow: /sounds/*
-Disallow: /system/*
-Disallow: /avatars/*
-Disallow: /headers/*