Update ExchangeTokenRequestTests.swift from review

Co-authored-by: Nick Cooke <36927374+ncooke3@users.noreply.github.com>

ExchangeTokenRequestTests.swift

@@ -42,7 +42,6 @@ class ExchangeTokenRequestTests: XCTestCase {
       location: kLocation,
       tenantId: kTenantID
     )
-    _ = app
 
     let request = ExchangeTokenRequest(
       idToken: kIdToken,