Replace internal `ShouldDescendExcludedDir` with upstream `c/storage` implementation

PR container-libs#1006 adds ShouldDescendExcludedDir to c/storage/pkg/fileutils.PatternMatcher and fixes archive.TarWithOptions to use it.

Once that merges and buildah vendors the updated c/storage, we should:

• Remove internal/excludes/ package and use PatternMatcher.ShouldDescendExcludedDir() directly
• Update copier/copier.go and add.go to call the upstream method

Depends on: container-libs#1006