PTranform name uniqueness javadoc

Is this doc about PTransform `name` contrary about uniqueness:
* https://github.com/apache/incubator-beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/PTransform.java#L198
* https://github.com/apache/incubator-beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/PTransform.java#L84

Imported from Jira [BEAM-861](https://issues.apache.org/jira/browse/BEAM-861). Original Jira may contain additional context.
Reported by: ravwojdyla.

Compare the PTransform javadoc at sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/PTransform.java lines 84 and 198, following the linked references first. Resolve whether the statements about name uniqueness conflict, then update the documentation so the uniqueness guidance is consistent.

Written by the indexing model from the issue text.