Add missing migrations for ea_sea_levels

I'm not sure why these migrations were required. Test thoroughly after 
deploying this one.

``` ALTER TABLE "ea_sea_levels_measurement" ALTER COLUMN "datetime" DROP 
DEFAULT; ALTER TABLE "ea_sea_levels_measurement" ALTER COLUMN "measurement"
DROP DEFAULT; ALTER TABLE "ea_sea_levels_station" ALTER COLUMN
"chart_datum_offset" DROP DEFAULT; ALTER TABLE "ea_sea_levels_station" DROP
CONSTRAINT ea_sea_le_location_id_1f9d264fb849759f_fk_locations_location_id; 
ALTER TABLE "ea_sea_levels_station" ADD CONSTRAINT 
ea_sea_le_location_id_70a2fb63b8676ead_fk_locations_location_id FOREIGN KEY
("location_id") REFERENCES "locations_location" ("id") DEFERRABLE INITIALLY
DEFERRED; ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "location_id" DROP 
DEFAULT; ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "site_datum" DROP 
DEFAULT; ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "station_id" DROP 
DEFAULT; ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "station_name" DROP 
DEFAULT;
```

[#77272214]