make filestream not set async options

[GarrettBeatty]

reverts #4264. its the same performance with or without this configuration. but with it was seeing below flaky tests

 Failed ConcurrentWrites_SequentialOrder_LargeParts_VerifyEveryByte [250 ms]
  Error Message:
   CollectionAssert.AreEqual failed. Part 2 data corrupted(Element at index 0 do not match.)    
  Stack Trace:
     at AWSSDK.UnitTests.FilePartDataHandlerConcurrencyTests.VerifyAllBytes(Byte[] fileData, Int32 partSize, Int32 partCount) in C:\dev\repos\aws-sdk-net\sdk\test\Services\S3\UnitTests\Custom\FilePartDataHandlerConcurrencyTests.cs:line 145
   at AWSSDK.UnitTests.FilePartDataHandlerConcurrencyTests.<ConcurrentWrites_SequentialOrder_LargeParts_VerifyEveryByte>d__8.MoveNext() in C:\dev\repos\aws-sdk-net\sdk\test\Services\S3\UnitTests\Custom\FilePartDataHandlerConcurrencyTests.cs:line 194
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.ThreadOperations.ExecuteWithAbortSafety(Action action)

rror Message:
   Assert.AreEqual failed. Expected:<3147352>. Actual:<3146328>. File size mismatch
  Stack Trace:
     at AWSSDK.UnitTests.FilePartDataHandlerConcurrencyTests.VerifyVaryingSizeBytes(Byte[] fileData, ValueTuple`3[] partDefinitions) in C:\dev\repos\aws-sdk-net\sdk\test\Services\S3\UnitTests\Custom\FilePartDataHandlerConcurrencyTests.cs:line 155
   at AWSSDK.UnitTests.FilePartDataHandlerConcurrencyTests.<ConcurrentWrites_MixedScenario_SmallAndLargeParts_VerifyEveryByte>d__18.MoveNext() in C:\dev\repos\aws-sdk-net\sdk\test\Services\S3\UnitTests\Custom\FilePartDataHandlerConcurrencyTests.cs:line 362
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.ThreadOperations.ExecuteWithAbortSafety(Action action)


Failed!  - Failed:     1, Passed:  1498, Skipped:     0, Total:  1499, Duration: 1 m 9 s - AWSSDK.UnitTests.S3.NetFramework.dll (net472)

after fix

=======================================
FINAL RESULTS: 0 failures out of 100 runs (0% failure rate)

dry run cbb983fc-a6ba-4b41-9661-4ab1ffcebe37