#584 System::GetHostName unused

[Oliver Schneider]

The function bool System::GetHostName(char name[255]) (aka gdcm::System::GetHostName) from Source/Common/gdcmSystem.cxx is superfluous, it appears.

The header even declares its visibility as static, but there's a test for the function inside Testing/Source/Common/Cxx/TestSystem1.cxx. Other than that, it's unused.

Therefore it should be removed.