TT#53701 Demote NGCP::Panel to a recommends in Build.PL

For the same reason we demoted the Debian dependency from a Depends to a
Recommends, because the NGCP::API do not necessarily need an ngcp-panel
instance running on the same host, we match the perl module metadata.

Change-Id: I43fe985c34db1e3206b607648028389ad0b93c09

Build.PL

@@ -9,8 +9,10 @@ my $builder = Module::Build->new(
         'IO::Socket::SSL'   => 0,
         'JSON'              => 0,
         'LWP::UserAgent'    => 0,
-        'NGCP::Panel'       => 0.01,
         'Readonly'          => 0,
     },
+    recommends        => {
+        'NGCP::Panel'       => 0,
+    },
 );
 $builder->create_build_script;