PUP-2040/PE-3113 Remove symlink-ignore tests for symlinkless OSes

Before this commit, the spec tests checked for symlink-ignore behavior on all
OSes. After this commit, the spec tests only check symlink-ignore
behavior on OSes that have symlinks.
Merge pull request #3018 from andersonmills/fix/master/PUP2040-fix_symlink_testing_on_windows

PUP-2040/PE-3113 Remove symlink-ignore tests for symlinkless OSes