Remove warning in download_tarball (#34549)

lib/spack/spack/binary_distribution.py

@@ -1576,10 +1576,6 @@ def download_tarball(spec, unsigned=False, mirrors_for_spec=None):
             )
         )
 
-    tty.warn(
-        "download_tarball() was unable to download "
-        + "{0} from any configured mirrors".format(spec)
-    )
     return None