This reverts commit fa6d921e.

Reason: Not a fan of such massive changes. We usually close such changes
if made to Rails master as a pull request. Following the same principle
here and reverting.

[ci skip]

For future reference, this is the regex I used: ^\s*#\s*\n(?!\s*#). Replace
with the first match, and voilà! Note that the regex matches a little bit too
much, so you probably want to `git add -i .` and go through every single diff
to check if it actually should be changed.

Closes #4441 if Active Record is disabled assets are delivered correctly

Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

Based on the implementation on the 2-3-stable branch, patches by Hongli
Lai <hongli@phusion.nl>, and helpful suggestions from José Valim.

Hongli Lai's patches included locking around the request cycle; this is
now handled by Rack::Lock (https://github.com/rack/rack/issues/issue/87/).

[#2873]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>