[test] Re-enable end2end test on Windows now that EE is rolled out (#38096)

Re-enables a test, disabled in https://github.com/grpc/grpc/pull/22333. Now that the Windows EventEngine is rolled out, this failure shouldn't be a problem anymore.

Closes #38096

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/38096 from drfloob:fix-b-148110727 4f5fb321bd
PiperOrigin-RevId: 696323903

test/core/end2end/tests/disappearing_server.cc

@@ -26,7 +26,6 @@
 #include "src/core/util/time.h"
 #include "test/core/end2end/end2end_tests.h"
 
-#ifndef GPR_WINDOWS  // b/148110727 for more details
 namespace grpc_core {
 
 static void OneRequestAndShutdownServer(CoreEnd2endTest& test) {
@@ -77,4 +76,3 @@ CORE_END2END_TEST(CoreClientChannelTest, DisappearingServer) {
 }
 
 }  // namespace grpc_core
-#endif  // GPR_WINDOWS