www/firefox: disable system ICU on /quarterly after 5ed442f26305

checking for icu-i18n >= 71.1... no
ERROR: Package dependency requirement 'icu-i18n >= 71.1' could not be satisfied.
ERROR: Package 'icu-i18n' has version '70.1', required version is '>= 71.1'

> Script "configure" failed unexpectedly.

Reported by: pkg-fallout