Clarify that only Error Prone's @Immutable is checked
Clarify that only Error Prone's @Immutable is checked

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=113215613

Anish2/error-prone,cushon/error-prone,cushon/error-prone,Anish2/error-prone,google/error-prone,google/error-prone,Anish2/error-prone,Anish2/error-prone,cushon/error-prone,cushon/error-prone