refactor(@angular-devkit/build-angular): remove deprecated karma builder environment option

BREAKING CHANGE:

Remove deprecated karma builder `environment` option

Author: alan-agius4

packages/angular_devkit/build_angular/src/karma/schema.json

@@ -59,11 +59,6 @@
       },
       "additionalProperties": false
     },
-    "environment": {
-      "type": "string",
-      "description": "Defines the build environment.",
-      "x-deprecated": "This option has no effect."
-    },
     "include": {
       "type": "array",
       "items": {