Fix encoding names and remove test for unsupported encoding

--- test_iconv.lua.orig	Tue Oct 25 21:39:29 2016
+++ test_iconv.lua	Tue Oct 25 21:39:51 2016
@@ -93,9 +93,8 @@ function check_one(to, from, text)
 end
 
 check_one(termcs, "iso-8859-1", iso88591)
-check_one(termcs, "utf8", utf8)
-check_one(termcs, "utf16", utf16)
-check_one(termcs, "EBCDIC-CP-ES", ebcdic)
+check_one(termcs, "utf-8", utf8)
+check_one(termcs, "utf-16", utf16)
 
 
 -- The library must never crash the interpreter, even if the user tweaks
