Remove policy nesting errors (#7449)

Policy nesting has been supported for a while
now, we should remove references of code and
docs indicating nesting is not allowed anymore.

docs/bucket/policy/README.md

@@ -1,39 +0,0 @@
-## Access Policy
-
-This package implements parsing and validating bucket access policies based on Access Policy Language specification - http://docs.aws.amazon.com/AmazonS3/latest/dev/access-policy-language-overview.html
-
-### Supports following effects.
-
-    Allow
-    Deny
-
-### Supports following set of operations.
-
-    s3:GetObject
-    s3:ListBucket
-    s3:PutObject
-    s3:GetBucketLocation
-    s3:DeleteObject
-    s3:AbortMultipartUpload
-    s3:ListBucketMultipartUploads
-    s3:ListMultipartUploadParts
-
-### Supports following conditions.
-
-    StringEquals
-    StringNotEquals
-    StringLike
-    StringNotLike
-    IpAddress
-    NotIpAddress
-
-Supported applicable condition keys for each conditions.
-
-    s3:prefix
-    s3:max-keys
-    aws:Referer
-    aws:SourceIp
-
-### Nested policy support.
-
-Nested policies are not allowed.