Enhance policy handling to support SSE and WORM (#5790)

- remove old bucket policy handling
- add new policy handling
- add new policy handling unit tests

This patch brings support to bucket policy to have more control not
limiting to anonymous.  Bucket owner controls to allow/deny any rest
API.

For example server side encryption can be controlled by allowing
PUT/GET objects with encryptions including bucket owner.

cmd/object-api-errors.go

@@ -366,13 +366,6 @@ func (e PolicyNesting) Error() string {
 	return "New bucket policy conflicts with an existing policy. Please try again with new prefix."
 }
 
-// PolicyNotFound - policy not found
-type PolicyNotFound GenericError
-
-func (e PolicyNotFound) Error() string {
-	return "Policy not found"
-}
-
 // UnsupportedMetadata - unsupported metadata
 type UnsupportedMetadata struct{}
 
@@ -396,15 +389,6 @@ func isErrIncompleteBody(err error) bool {
 	return false
 }
 
-// isErrBucketPolicyNotFound - Check if error type is BucketPolicyNotFound.
-func isErrBucketPolicyNotFound(err error) bool {
-	switch err.(type) {
-	case PolicyNotFound:
-		return true
-	}
-	return false
-}
-
 // isErrObjectNotFound - Check if error type is ObjectNotFound.
 func isErrObjectNotFound(err error) bool {
 	switch err.(type) {