http: move writeHeader to end-of-life #706

Job	Run time
Build slim tarball	1m 29s
aarch64-linux: with shared libraries	23m 25s
x86_64-linux: with shared libraries	27m 42s
x86_64-darwin: with shared libraries	1h 50m 29s
aarch64-darwin: with shared libraries	28m 38s
	3h 11m 43s

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