[KYUUBI #5624] [UI] Remove npm run build warning about NODE_ENV=produ…

…ction

### _Why are the changes needed?_

Before this PR, when we run `npm run build` to build production dist will meet:
```log
NODE_ENV=production is not supported in the .env file. Only NODE_ENV=development is supported to create a development build of your project. If you need to set process.env.NODE_ENV, you can set it in the Vite config instead.
```

So, let's remove `NODE_ENV=production` in `.env.production`, it's non-used.
### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [x] [Run test](https://kyuubi.readthedocs.io/en/master/contributing/code/testing.html#running-tests) locally before make a pull request

### _Was this patch authored or co-authored using generative AI tooling?_

No

Closes #5624 from zwangsheng/ui/remove_build_warning.

Closes #5624

20c21fc [zwangsheng] [UI] Remove npm run build warning about NODE_ENV=production

Authored-by: zwangsheng <[email protected]>
Signed-off-by: Cheng Pan <[email protected]>

kyuubi-server/web-ui/.env.production

@@ -13,6 +13,4 @@
  # See the License for the specific language governing permissions and
  # limitations under the License.
 
-NODE_ENV=production
-
 VITE_APP_DEV_WEB_URL='/'