remove util-env.lua due to interfering argv handling

The stricter behavior of table.insert() since Lua 5.2.2 causes the
import of util-env.lua to fail. Since the argument handling is specific
to Context we now ship the extended set without the file.

Thanks to: Karl Berry, Hironoir Kitagawa, Akira Kakuto for discovering /
reporting the issue!
update readme and news, bump version