ui: only set query url to localhost if config option is falsy

The `THANOS_QUERY_URL` constant is already assigned to `{{ .queryURL }}` in `public/index.html`.
Remove this comparison, as it causes the `--alert.query-url` command line option to have no effect whatsoever.

Fixes thanos-io#6370

Signed-off-by: Steffen Neubauer <stefreak@googlemail.com>

pkg/ui/react-app/src/thanos/config.ts

@@ -1,6 +1,6 @@
 declare const THANOS_QUERY_URL: string;
 
 export let queryURL = THANOS_QUERY_URL;
-if (queryURL === '' || queryURL === '{{ .queryURL }}') {
+if (!queryURL) {
   queryURL = 'http://localhost:10902';
 }