Remove deprecated `shell_streams` and `_parent_header` shims #3971

Job	Run time
check_release	36s
Make SDist	24s
test_without_debugpy (ubuntu-latest, 3.10)	38s
Test Prereleases	43s
Test Lint	42s
link_check	43s
Test Minimum Versions	42s
test_docs	32s
build (ubuntu-latest, qt6, 3.10)	43s
build (ubuntu-latest, qt5, 3.14)	43s
build (ubuntu-latest, qt5, 3.10)	41s
build (ubuntu-latest, qt6, 3.11)	42s
build (windows-latest, qt5, 3.10)	41s
build (ubuntu-latest, qt6, 3.13)	43s
build (ubuntu-latest, qt6, 3.12)	43s
build (windows-latest, qt6, 3.11)	42s
build (windows-latest, qt6, 3.10)	37s
build (macos-latest, qt5, 3.10)	49s
build (windows-latest, qt6, 3.12)	34s
build (windows-latest, qt6, 3.13)	41s
build (windows-latest, qt6, pypy-3.11)	32s
build (ubuntu-latest, qt6, pypy-3.11)	42s
build (macos-latest, qt5, 3.14)	48s
build (macos-latest, qt6, 3.10)	32s
build (windows-latest, qt5, 3.14)	42s
build (macos-latest, qt6, 3.13)	44s
build (macos-latest, qt6, 3.11)	45s
build (macos-latest, qt6, 3.12)	44s
build (macos-latest, qt5, pypy-3.11)	51s
build (windows-latest, qt5, pypy-3.11)	33s
build (macos-latest, qt6, pypy-3.11)	48s
build (ubuntu-latest, qt5, pypy-3.11)	43s
Install from SDist and Test	1s
coverage	1s
	21m 45s

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