We currently have two lists of "proxy" or "fetcher" environment exports.
Make the one in utils match the one on the fetcher which has a more complete
list of variables now.
(Bitbake rev: f9165a798a307a6f0fee120d5c3de660d3a44ae8)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>