DERBY-6276; Convert lang/DB2IsolationLevels.sql to JUnit
  giving svn delete another go to remove master and .sql. Also removing test from derbylang.


git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1519870 13f79535-47bb-0310-9956-ffa450edef68