support/script/scancpan: remove duplicated dependency

Dependencies from metacpan comes as a list of modules which is
transformed in a list of distribution for BR.  Different modules could
be included in the same distribution, so duplication is possible.

This can for example be seen with the HTTP-Daemon module, which would
get two times the dependencies on HTTP-Message without this commit.

[Thomas: slightly extend commit log.]

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
user guest
defconfig
network interface eth0
demo

set BR2_ROOTFS_OVERLAY with $(BR2_EXTERNAL)/overlay/
mojo skeleton

$ mojo generate app