lib/curl: clean up surperfluous types

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/curl: clean up CurlMailRequest::init

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/curl: remove indirect creation of basic requests

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>