Java no-build-system test: switch to single-file diagnostics.expected format

Author: smowton

java/ql/integration-tests/all-platforms/java/diagnostics/no-build-system/diagnostics.expected

@@ -0,0 +1 @@
+{"markdownMessage": "Could not find a Gradle, Maven or Ant top-level project to build. Please [TODO](supply a manual build command)", "severity": "error", "source": {"extractorName": "java", "id": "java/autobuilder/no-build-command", "name": "No build command found"}, "visibility": {"cliSummaryTable": true, "statusPage": true, "telemetry": true}}