[O] Code Block Headers Appear in Export

[Alan Lue]

I find that code block header arguments specified with `#+HEADERS:'
consistently appear in the exported document. For example, exporting the
following document to PDF or HTML will include the "exports" header in
the output:

* Manifestation of Problem

  Look, our headers appear in the export:
  #+headers: :exports both
  #+BEGIN_SRC R :results output
    sd(rnorm(50))
  #+END_SRC

How does one suppress the export of header arguments? For reference, I'm
using Org-mode version 7.9.1.