Given that ICU is a set of lively developed libraries, that ICU 50.1
has been released on 2012-11-05, and PHP 7.4 is scheduled to be
released seven years after it, we consider it appropriate to ditch
these legacy versions.
Particularly, that would be a reasonable groundwork to implement part
two of the “Deprecate and remove INTL_IDNA_VARIANT_2003” RFC[1], namely
to default idn_to_ascii()'s and idn_to_utf8()'s $variant parameter to
INTL_IDNA_VARIANT_UTS46, which is not defined in ICU < 4.6.
See also the related discussion on internals@[2].
[1] <https://wiki.php.net/rfc/deprecate-and-remove-intl_idna_variant_2003>
[2] <http://news.php.net/php.internals/101626>ff
