HTTP: simplifed r.subrequest() code. #29

Job	Run time
buildbot / check-if-allowed	1s
buildbot / print	1m 2s
buildbot / test (alpine-3.19, amd64)	6m 6s
buildbot / msan	4m 59s
buildbot / asan (njs)	3m 56s
buildbot / test (alpine-3.19, arm64)	3m 57s
buildbot / asan (quickjs)	4m 52s
buildbot / test (amazonlinux-2, amd64)	3m 34s
buildbot / test (amazonlinux-2, arm64)	2m 33s
buildbot / test (amazonlinux-2023, amd64)	7m 49s
buildbot / test (amazonlinux-2023, arm64)	5m 51s
buildbot / test (debian-11, amd64)	3m 56s
buildbot / test (debian-11, arm64)	2m 56s
buildbot / test (debian-12, amd64)	4m 47s
buildbot / test (debian-12, arm64)	3m 25s
buildbot / test (freebsd-14, amd64)	4m 7s
buildbot / test (rhel-7, amd64)	2m 29s
buildbot / test (rhel-8, amd64)	4m 15s
buildbot / test (rhel-8, arm64)	2m 42s
buildbot / test (rhel-9, amd64)	7m 51s
buildbot / test (rhel-9, arm64)	5m 20s
buildbot / test (sles-12, amd64)	2m 17s
buildbot / test (ubuntu-20.04, amd64)	4m 20s
buildbot / test (ubuntu-20.04, arm64)	2m 56s
buildbot / test (ubuntu-22.04, amd64)	7m 15s
buildbot / test (ubuntu-22.04, arm64)	5m 24s
buildbot / test (ubuntu-23.10, amd64)	7m 43s
buildbot / test (ubuntu-23.10, arm64)	5m 28s
buildbot / test (debian-12, x86)	5m 22s
	2h 7m 13s

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