move Backend interface to backend package

internal/backend/s3/config.go

@@ -6,9 +6,9 @@ import (
 	"path"
 	"strings"
 
+	"github.com/restic/restic/internal/backend"
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
-	"github.com/restic/restic/internal/restic"
 )
 
 // Config contains all configuration necessary to connect to an s3 compatible
@@ -94,7 +94,7 @@ func createConfig(endpoint, bucket, prefix string, useHTTP bool) (*Config, error
 	return &cfg, nil
 }
 
-var _ restic.ApplyEnvironmenter = &Config{}
+var _ backend.ApplyEnvironmenter = &Config{}
 
 // ApplyEnvironment saves values from the environment to the config.
 func (cfg *Config) ApplyEnvironment(prefix string) {