drop __diefunc compat function

It was dropped from portage almost 2 years ago and was last used about 6
years ago, therefore compatibility is no longer needed.

This also fixes a bug where die was called with 3 string arguments (from
a multiline error message in the WORKDIR fallback support for EAPI >= 4)
which were shifted out of scope due to the old code used to shift the
arguments passed from diefunc whiched called die.