Deflake HTTP2ConnectionTests/testSimpleGetRequest (#851)

Motivation:

testSimpleGetRequest asserts right after submitting the request for
execution that no streams have been closed. While unlikely there's
nothing to prevent this assertion from failing (and indeed it has
failed): the request may have executed immediately and the stream closed
before checking the delegate.

Modifications:

- Remove the assertion

Result:

Tests are less flaky

Author: glbrntt

Tests/AsyncHTTPClientTests/HTTP2ConnectionTests.swift

@@ -115,7 +115,6 @@ class HTTP2ConnectionTests: XCTestCase {
 
         http2Connection.executeRequest(requestBag)
 
-        XCTAssertEqual(delegate.hitStreamClosed, 0)
         var maybeResponse: HTTPClient.Response?
         XCTAssertNoThrow(maybeResponse = try requestBag.task.futureResult.wait())
         XCTAssertEqual(maybeResponse?.status, .ok)