Replace proj/Units enum with typedef

src/ol/format/MVT.js

@@ -13,7 +13,6 @@ import Point from '../geom/Point.js';
 import Polygon from '../geom/Polygon.js';
 import Projection from '../proj/Projection.js';
 import RenderFeature from '../render/Feature.js';
-import Units from '../proj/Units.js';
 import {assert} from '../asserts.js';
 import {get} from '../proj.js';
 import {inflateEnds} from '../geom/flat/orient.js';
@@ -52,7 +51,7 @@ class MVT extends FeatureFormat {
      */
     this.dataProjection = new Projection({
       code: '',
-      units: Units.TILE_PIXELS,
+      units: 'tile-pixels',
     });
 
     /**