packaging: drop yad download code

yad is now provided by EPEL repository and we don't need
to manually download and install it.

Change-Id: I1666d59a4011671f76a7f142a36bb70412beb4af
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
(cherry picked from commit 26f0141c46e955503d95323e4f8258f5d46a772f)