Removed probably unnecessary code of Sysfs driver

[ignaciocaramba]

Fixes #2131
When using the SysFs driver the following exception gets thrown when pressing the button connected to the pin:

Unhandled exception. System.IO.IOException: Error while trying to seek in value file.
   at System.Device.Gpio.Drivers.SysFsDriver.WasEventDetected(Int32 pollFileDescriptor, Int32 valueFileDescriptor, Int32& pinNumber, CancellationToken cancellationToken)
   at System.Device.Gpio.Drivers.SysFsDriver.DetectEvents()
   at System.Threading.Thread.StartHelper.Callback(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.Thread.StartCallback()

After removing the code, the exception is not thrown.

Microsoft Reviewers: Open in CodeFlow

[ignaciocaramba]

@dotnet-policy-service agree

[krwq]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pgrawehr]

Appears to be working, and IIRC I considered removing that before. Should be fine until we find a reason to keep it.