tests: remove unused xds-failover test code (#37963)

Commit Message: tests: remove unused xds-failover test code
Additional Description:
tests: remove unused xds-failover test code

Risk Level: low - tests only
Testing: N/A
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A

Signed-off-by: Adi Suissa-Peleg <adip@google.com>

Author: adisuissa

test/extensions/config_subscription/grpc/xds_failover_integration_test.cc

@@ -183,14 +183,6 @@ class XdsFailoverAdsIntegrationTest : public AdsDeltaSotwIntegrationSubStatePara
     RELEASE_ASSERT(result, result.message());
   }
 
-  // Waits for a failover source connected and immediately disconnects.
-  void failoverConnectionFailure() {
-    AssertionResult result = xds_upstream_->waitForHttpConnection(*dispatcher_, xds_connection_);
-    RELEASE_ASSERT(result, result.message());
-    result = xds_connection_->close();
-    RELEASE_ASSERT(result, result.message());
-  }
-
   envoy::config::endpoint::v3::ClusterLoadAssignment
   buildClusterLoadAssignment(const std::string& name) {
     return ConfigHelper::buildClusterLoadAssignment(