Don't put US-specific units in und

[robertbastian]

This was a side effect of und expanding to en-Latn-US. #7918 preserves behaviour, but makes it explicit that we choose US as the default region.

meter and kilogram become core units, foot and pound become extended units.

This significantly reduces data size, because the US's special-snowflaking was not great for fallback

-units/names/area/core/v1, <lookup>, 32936B, 2233 identifiers
+units/names/area/core/v1, <lookup>, 16794B, 1112 identifiers

-units/names/area/extended/v1, <lookup>, 25723B, 2286 identifiers
+units/names/area/extended/v1, <lookup>, 15796B, 1315 identifiers

-units/names/length/core/v1, <lookup>, 34216B, 2375 identifiers
+units/names/length/core/v1, <lookup>, 24255B, 1684 identifiers

-units/names/length/extended/v1, <lookup>, 26077B, 2403 identifiers
+units/names/length/extended/v1, <lookup>, 25257B, 2152 identifiers

-units/names/mass/core/v1, <lookup>, 33003B, 3101 identifiers
+units/names/mass/core/v1, <lookup>, 17354B, 1658 identifiers

-units/names/mass/extended/v1, <lookup>, 16789B, 1445 identifiers
+units/names/mass/extended/v1, <lookup>, 10676B, 935 identifiers

-units/names/volume/core/v1, <lookup>, 38249B, 2898 identifiers
+units/names/volume/core/v1, <lookup>, 21271B, 1546 identifiers

-units/names/volume/extended/v1, <lookup>, 62909B, 5710 identifiers
+units/names/volume/extended/v1, <lookup>, 40657B, 3546 identifiers

Changelog

N/A