Clean up host quantile helpers #14823

Job	Run time
Build libxgboost4j.dylib for MacOS (Apple Silicon)	1m 5s
Build and test JVM packages (windows-latest)	8m 29s
Build libxgboost4j.so targeting glibc 2.17 (arch x86_64, runner linux-amd64-cpu)	2m 8s
Build and test JVM packages (macos-15-intel)	9m 19s
Configure variables for CI	9s
Build libxgboost4j.dylib for MacOS (Intel)	2m 28s
Build libxgboost4j.so targeting glibc 2.17 (arch aarch64, runner linux-arm64-cpu)	2m 18s
Build and test JVM packages (Linux, Scala 2.12)	10m 44s
Build libxgboost4j.so with CUDA	9m 27s
Build and test JVM packages (Linux, Scala 2.13)	5m 41s
Test JVM packages with CUDA (Scala 2.13)	8m 6s
Test JVM packages with CUDA (Scala 2.12)	7m 59s
Deploy JVM packages to S3 (gpu, Scala 2.12)	2m 53s
Deploy JVM packages to S3 (cpu, Scala 2.13)	51s
Deploy JVM packages to S3 (cpu, Scala 2.12)	53s
Deploy JVM packages to S3 (gpu, Scala 2.13)	2m 52s
	1h 15m 22s

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