Remove bogus implementations of ApplyGetContainingDigests

At the call site we could just check the return value of VirtualApply()
to see whether this operation is actually implemented by the files in
question.

Author: EdSchouten

pkg/filesystem/virtual/placeholder_file.go

@@ -3,7 +3,6 @@ package virtual
 import (
 	"context"
 
-	"github.com/buildbarn/bb-storage/pkg/digest"
 	"github.com/buildbarn/bb-storage/pkg/filesystem"
 
 	"google.golang.org/grpc/codes"
@@ -52,8 +51,6 @@ func (placeholderFile) VirtualApply(data any) bool {
 	switch p := data.(type) {
 	case *ApplyUploadFile:
 		p.Err = status.Error(codes.InvalidArgument, "This file cannot be uploaded, as it is a placeholder")
-	case *ApplyGetContainingDigests:
-		p.ContainingDigests = digest.EmptySet
 	default:
 		return false
 	}

pkg/filesystem/virtual/pool_backed_file_allocator.go

@@ -351,8 +351,6 @@ func (f *fileBackedFile) VirtualApply(data any) bool {
 		p.Err = syscall.EINVAL
 	case *ApplyUploadFile:
 		p.Digest, p.Err = f.uploadFile(p.Context, p.ContentAddressableStorage, p.DigestFunction, p.WritableFileUploadDelay)
-	case *ApplyGetContainingDigests:
-		p.ContainingDigests = digest.EmptySet
 	case *ApplyGetBazelOutputServiceStat:
 		p.Stat, p.Err = f.getBazelOutputServiceStat(p.DigestFunction)
 	case *ApplyAppendOutputPathPersistencyDirectoryNode: