remove unused header files #31

Job	Run time
macOS / release / homebrew-clang	6m 2s
Windows / release / msvc	25m 0s
macOS / debug / homebrew-clang	4m 38s
Windows / release / clang-cl	23m 22s
macOS / release / system-clang	5m 34s
Windows / release / llvm	25m 12s
macOS / debug / system-clang	4m 21s
Windows / debug / msvc	30m 3s
Windows / debug / clang-cl	24m 21s
Windows / debug / llvm	28m 40s
	2h 57m 13s

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