remove unused header files #39

Job	Run time
macOS / release / homebrew-clang	5m 26s
macOS / debug / homebrew-clang	7m 41s
macOS / release / system-clang	4m 57s
macOS / debug / system-clang	5m 36s
Windows / release / msvc	32m 59s
Windows / release / clang-cl	28m 2s
Windows / release / llvm	17m 17s
Windows / debug / msvc	24m 6s
Windows / debug / clang-cl	18m 20s
Windows / debug / llvm	20m 20s
	2h 44m 44s

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