samples: do not use the mirror by default

As the mirror is always tried first, and the default is my server,
it means every download will first hit my server. As I do not have
much mirrored there, it means a lot of time is lost.

Disable use of the mirror for all samples, except the one that does
need it for the uClibc snapshot.

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

 This is NOT the official version of dialog.  This version has been

 significantly modified from the original.  It is for use by the Linux

 kernel configuration script.  Please do not bother Savio Lam with 

 questions about this program.