thread pool is actually not used in tests

Author: dnadoba

Tests/AsyncHTTPClientTests/RequestBagTests.swift

@@ -771,16 +771,13 @@ final class RequestBagTests: XCTestCase {
     }
 }
 
-import NIOPosix
-
 extension HTTPClient.Task {
     convenience init(
         eventLoop: EventLoop,
         logger: Logger
     ) {
-        lazy var threadPool = NIOThreadPool(numberOfThreads: 1)
         self.init(eventLoop: eventLoop, logger: logger) {
-            threadPool
+            preconditionFailure("thread pool not needed in tests")
         }
     }
 }