[MSHARED-860] Deprecate unnecessary Java7Support

[roxspring]

I believe that Java 7 has been a minimum requirement for almost a year so here's some overdue cleanup:

• Call java.nio.file.Files utility methods directly rather than via reflection
• Move createSymbolicLink() utility to FileUtils
• Deprecate Java7Support and call java.nio.file.Files methods directly

MSHARED-860

[jira-importer]

Resolve #305