(PUP-836) Remove Win32::Security.elevated_security

• Refactor Puppet::Util::Windows::Process to implement new method elevated_security? that was in win32-security gem
• Refactor get_token_information to return an FFI::MemoryPointer buffer instead of a parsed structure, since GetTokenInformation is a generic call that can return many structure types, including TOKEN_ELEVATION.
• Remove any reliance on win32-security gem from user.rb
• Adjust tests accordingly