Use dryRun unstead of importMode when making api call to old tracker API

Since this is the accepted param

src/pages/TEIImport/form-helper.js

@@ -29,7 +29,7 @@ const onImport =
         const apiBaseUrl = `${baseUrl}/api/`
         const endpoint = 'trackedEntityInstances.json'
         const params = [
-            `importMode=${dryRun ? 'VALIDATE' : 'COMMIT'}`,
+            `dryRun=${dryRun}`,
             `identifier=${identifier}`,
             `importReportMode=${importReportMode}`,
             `preheatMode=${preheatMode}`,