remove unused header files #29

Job	Run time
macOS / release / homebrew-clang	5m 37s
Windows / release / msvc	25m 59s
macOS / debug / homebrew-clang	5m 41s
Windows / release / clang-cl	25m 2s
macOS / release / system-clang	6m 28s
Windows / release / llvm	26m 56s
Windows / debug / msvc	26m 1s
macOS / debug / system-clang	3m 26s
Windows / debug / clang-cl	24m 22s
Windows / debug / llvm	26m 7s
	2h 55m 39s

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