Revert "Add tests for fluent"

This reverts commit 8ec9500.

Author: dxvladislavvolkov

packages/devextreme-cli/testing/constants.js

@@ -28,7 +28,6 @@ exports.viewports = {
 };
 
 exports.themes = {
-    fluent: 'fluent.blue',
     material: 'material.blue',
     generic: 'generic'
 };