Some rework of Equivalence javadocs. Remove a message that no longer applies there.
Some rework of Equivalence javadocs. Remove a message that no longer applies there.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=147899167

DavesMan/guava,typetools/guava,typetools/guava,google/guava,DavesMan/guava,EdwardLee03/guava,rgoldberg/guava,berndhopp/guava,mosoft521/guava,mosoft521/guava,EdwardLee03/guava,berndhopp/guava,Xaerxess/guava,xasx/guava,mosoft521/guava,rgoldberg/guava,google/guava,xasx/guava,google/guava,Xaerxess/guava