Use 2020 geographies instead of the 2010 for EPHT Subcounty

[depryf]

The 2010 won't be used anymore, we can stop loading them entirely.

The current variables are

• 9993 epht2010GeoId5k EPHT 2010 GEO ID 5K
• 9994 epht2010GeoId20k EPHT 2010 GEO ID 20K
• 9995 epht2010GeoId50k EPHT 2010 GEO ID 50K

They will be replaced by

• 9996 epht2020GeoId5k EPHT 2020 GEO ID 5K
• 9997 epht2020GeoId20k EPHT 2020 GEO ID 20K
• 9998 epht2020GeoId50k EPHT 2020 GEO ID 50K

CFD Squish issue 146.