scripts/functions: only use one download program

Currently, we use either wget or curl, whichever is installed.
In case both are installed, both are used. This means that it
takes a while trying all extensions.

Remove use of wget, and use only curl.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

reporter_name="Thomas Petazzoni"

reporter_url="http://www.free-electrons.com/"

reporter_comment="Very basic testing only"