namd: No need to delete stuff in build tree as it is thrown away at end

builder.sh

@@ -34,7 +34,6 @@ cp -r ../psfgen ./sb
 mkdir -p $out/lib/namd
 cp -r * $out/lib/namd
 cd ..
-rm -rf Linux-x86_64-g++
 
 mkdir -p $out/bin
 ln -s $out/lib/namd2 $out/bin/namd2