LibC: Revert localtime_r to use time zone information set by tzset

Now that tzset actually detects time zones, parties interested in time
zone offsets should invoke tzset.

Userland/Libraries/LibC/time.cpp

@@ -162,13 +162,7 @@ struct tm* localtime_r(const time_t* t, struct tm* tm)
     if (!t)
         return nullptr;
 
-    auto time_zone = TimeZone::current_time_zone();
-    auto time = AK::Time::from_seconds(*t);
-
-    if (auto offset = TimeZone::get_time_zone_offset(time_zone, time); offset.has_value())
-        time += AK::Time::from_seconds(offset->seconds);
-
-    time_to_tm(tm, time.to_seconds());
+    time_to_tm(tm, *t - timezone);
     return tm;
 }