BTreeMapTest: remove dependency on Java 7 class
BTreeMapTest: remove dependency on Java 7 class

pettermahlen/mapdb,binarytemple/mapdb,cocosli/mapdb,sumit784/mapdb,morfeo8marc/mapdb,codeaudit/mapdb,lamfire/mapdb,SleimanJneidi/mapdb,jankotek/mapdb,jankotek/MapDB,jankotek/MapDB,ffjiao/mapdb,jankotek/mapdb,hangum/mapdb,ringoluo/mapdb