backupsink: drop pretty.Formatter log that crashes on Azure errors

When closing the underlying writer in FileSSTSink.Flush failed, we
logged the error via pretty.Formatter, whose reflection walk dereferences
unexported fields. With Azure SDK errors that embed *http.Response and
internal buffers released by the SDK, this can dereference freed memory
and SIGSEGV. The error is already wrapped and returned to the caller, so
the warning was redundant.

Drop the warning (and the now-unused kr/pretty import).

Fixes #169668.

Release note (bug fix): Fixed a possible SIGSEGV when a backup encountered
a transient error writing to Azure Blob Storage.

Author: dt

pkg/backup/backupsink/BUILD.bazel

@@ -26,7 +26,6 @@ go_library(
         "//pkg/util/unique",
         "@com_github_cockroachdb_errors//:errors",
         "@com_github_gogo_protobuf//types",
-        "@com_github_kr_pretty//:pretty",
     ],
 )
 

pkg/backup/backupsink/file_sst_sink.go

@@ -25,7 +25,6 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/errors"
 	gogotypes "github.com/gogo/protobuf/types"
-	"github.com/kr/pretty"
 )
 
 var (
@@ -280,7 +279,6 @@ func (s *FileSSTSink) Flush(ctx context.Context) error {
 		return err
 	}
 	if err := s.out.Close(); err != nil {
-		log.Warningf(ctx, "failed to close write in FileSSTSink: % #v", pretty.Formatter(err))
 		return errors.Wrap(err, "writing SST")
 	}
 	wroteSize := s.sst.Meta.Size