remove unused header files #33

Job	Run time
macOS / release / homebrew-clang	6m 20s
Windows / release / msvc	17m 40s
macOS / debug / homebrew-clang	4m 19s
Windows / release / clang-cl	22m 35s
macOS / release / system-clang	4m 32s
Windows / release / llvm	24m 26s
macOS / debug / system-clang	3m 26s
Windows / debug / msvc	23m 12s
Windows / debug / clang-cl	21m 16s
Windows / debug / llvm	23m 14s
	2h 31m 0s

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