Fix Flat3Map entrySet remove ignoring the entry value

[rootvector2]

noticed Flat3Map.EntrySet.remove diverges from AbstractHashedMap: it removes on a key match alone, so entrySet().remove(entry) drops a mapping even when the entry value differs; guard with contains(obj) so only a full key-and-value match removes.

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[garydgregory]

Good one @rootvector2 , will merge 🚀 . We have many of these types of types which may suffer from the same issue. Would you please check other Maps? TY! In the future, don't edit changes.xml.

[rootvector2]

went through the other EntrySet.remove implementations: AbstractHashedMap and AbstractPatriciaTrie guard with contains(obj), TreeBidiMap (both views), AbstractDualBidiMap, PassiveExpiringMap and ListOrderedMap all check the value, StaticBucketMap compares entries via Node.equals (key and value), and ConcurrentReferenceHashMap delegates to remove(key, value). Flat3Map was the only one removing on key alone, so nothing else needs fixing. noted on changes.xml, will leave it out going forward. thanks for merging.