[Tizen] xwalk.gyp: Do not special-case virtual_root_provider_tizen.cc.

There is no need to put that file inside a "tizen==1" condition, files
terminating in _tizen.cc are automatically excluded from the build on
other platforms.
Merge pull request #2668 from rakuco/tizen-move-file-to-generic-list

[Tizen] xwalk.gyp: Do not special-case virtual_root_provider_tizen.cc.