Do not use needauth when only exporting code

Do not use needauth when only exporting code

We have a couple of converters (using Sweave and knitr to "tangle"
an intermediate file) that are used for exporting code chunks
contained in a .lyx file. Since the code is just exported to a text
file and is not executed, needauth is not necessary.

(cherry picked from commit 065e37e96ff37dd891e47aede84258fd9adf23cf)