Revert "UI: added milligram per cubic meter unit"

This reverts commit 3775208851.

ui-ngx/src/assets/locale/locale.constant-en_US.json

@@ -4535,7 +4535,6 @@
         "gram-per-cubic-centimeter": "Gram per cubic centimeter",
         "kilogram-per-square-meter": "Kilogram per square metre",
         "milligram-per-milliliter": "Milligram per milliliter",
-        "milligram-per-cubic-meter": "Milligram per cubic meter",
         "pound-per-cubic-foot": "Pound per cubic foot",
         "ounces-per-cubic-inch": "Ounces per cubic inch",
         "tons-per-cubic-yard": "Tons per cubic yard",

ui-ngx/src/assets/metadata/units.json

@@ -1316,11 +1316,6 @@
   "symbol": "mg/mL",
   "tags": ["concentration","mass per volume","mg/mL"]
 },
-{
-    "name": "unit.milligram-per-cubic-meter",
-    "symbol": "mg/m³",
-    "tags": ["concentration","mass per volume","mg/m³"]
-},
 {
   "name": "unit.pound-per-cubic-foot",
   "symbol": "lb/ft³",