news/slrn: fix crash with SIGSERV in the iconv_convert_string()

Back out r349278 that added --with-non-gnu-iconv trying to solve
our early iconv() inconsistences that are not actual anymore
as it now now correctly returns non-zero count of convertable symbols.

This fixes unsigned underflow in the slrn code turning
negative value to large positive leading to incorrect memory accesses later.

PR: 228502
Approved by: johans (maintainer timeout, 1 month)