[v1.x] fix license for blockingconcurrentqueue

[mseth10]

Currently 3rdparty/dmlc-core/include/dmlc/blockingconcurrentqueue.h is placed under two different licenses 2-clause BSD license and Apache-2.0 license + zlib license. As per the file, it should be under a single license 2-clause BSD license + zlib license

Master branch PR: #19909

[mxnet-bot]

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