accessibility/hyprsunset: correct #if condition of patch

The condition in the former patch makes the port use the date-tz
library of devel/date even when libc++ supports
std::chrono::current_zone, etc. Checking
_LIBCPP_HAS_NO_TIME_ZONE_DATABASE is enough and it won't be defined by
libstdc++.

Reported by: jbeich (via ports-committers)
Fixes: d9a1aaa98d16 (accessibility/hyprsunset: update to 0.3.1)