Drop a lot of -l options from xduplic-copier.

This gets rid of a lot of these:

 dpkg-shlibdeps: warning: package could avoid a useless dependency if /home/ian/things/Chiark-utils/chiark-utils.git/debian/tmp/chiark-utils-bin/usr/bin/xduplic-copier was not linked against libXt.so.6 (it uses none of the library's symbols)

On platforms without shared library support, it may be necessary to
edit the Makefile to put them back.