[dask] Remove dconcat. #11719

Job	Run time
Build libxgboost4j.so with CUDA	5m 56s
Build libxgboost4j.dylib for MacOS (Apple Silicon)	1m 41s
Build libxgboost4j.so targeting glibc 2.17 (arch aarch64, runner linux-arm64-cpu)	1m 35s
Build libxgboost4j.dylib for MacOS (Intel)	4m 38s
Build libxgboost4j.so targeting glibc 2.17 (arch x86_64, runner linux-amd64-cpu)	1m 54s
Build and test JVM packages (Linux, Scala 2.12)	10m 34s
Build and test JVM packages (Linux, Scala 2.13)	5m 19s
Build and test JVM packages (windows-latest)	10m 17s
Build and test JVM packages (macos-13)	11m 8s
Build docs for JVM packages	4m 41s
Test JVM packages with CUDA (Scala 2.12)	6m 0s
Test JVM packages with CUDA (Scala 2.13)	5m 53s
Deploy JVM packages to S3 (cpu)	7s
Deploy JVM packages to S3 (cpu)	7s
Deploy JVM packages to S3 (gpu)	8s
Deploy JVM packages to S3 (gpu)	9s
	1h 10m 7s

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