Do not install iso-8859-15, aspell ships the newer charset.

diff -Nrup a/Makefile.pre b/Makefile.pre
--- a/Makefile.pre	2004-12-22 04:55:19.000000000 +0100
+++ b/Makefile.pre	2026-10-22 17:22:14.902341524 +0200
@@ -4,7 +4,7 @@ lang = nds
 version = 0.01-0
 
 cwl_files = nds.cwl
-data_files = nds.dat nds_affix.dat nds_phonet.dat iso-8859-15.cset iso-8859-15.cmap
+data_files = nds.dat nds_affix.dat nds_phonet.dat
 doc_files = README README.iso COPYING Copyright
 extra_files = configure info Makefile.pre
 multi_files = lowsaxon.alias nds.multi