remove unused header files #22

Job	Run time
Ubuntu / Release / gcc	20m 13s
macOS / Release / homebrew-clang	6m 20s
Ubuntu / Debug / gcc	16m 8s
macOS / Debug / homebrew-clang	5m 14s
Ubuntu / Release / clang	16m 36s
macOS / Release / system-clang	6m 37s
Ubuntu / Debug / clang	12m 41s
macOS / Debug / system-clang	4m 12s
Windows / Release / cl	30m 30s
Windows / Release / clang	29m 12s
Windows / Release / clang-cl	24m 13s
Windows / Debug / cl	25m 43s
Windows / Debug / clang	25m 53s
Windows / Debug / clang-cl	24m 0s
	4h 7m 32s

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