Remove deprecated `shell_streams` and `_parent_header` shims #3973

Job	Run time
test_without_debugpy (ubuntu-latest, 3.10)	2m 8s
check_release	1m 39s
link_check	4m 24s
test_docs	45s
Make SDist	25s
Test Prereleases	2m 36s
Test Lint	57s
Test Minimum Versions	2m 40s
build (ubuntu-latest, qt5, pypy-3.11)	3m 37s
build (windows-latest, qt5, pypy-3.11)	4m 29s
build (ubuntu-latest, qt6, 3.12)	2m 41s
build (ubuntu-latest, qt5, 3.14)	2m 42s
build (ubuntu-latest, qt6, 3.10)	2m 40s
build (ubuntu-latest, qt6, 3.13)	2m 36s
build (ubuntu-latest, qt6, 3.11)	2m 32s
build (ubuntu-latest, qt6, pypy-3.11)	3m 43s
build (windows-latest, qt5, 3.10)	5m 12s
build (windows-latest, qt6, 3.10)	4m 33s
build (macos-latest, qt6, 3.10)	3m 2s
build (windows-latest, qt5, 3.14)	3m 51s
build (windows-latest, qt6, 3.13)	3m 36s
build (windows-latest, qt6, 3.12)	4m 47s
build (macos-latest, qt5, 3.14)	3m 6s
build (windows-latest, qt6, pypy-3.11)	4m 45s
build (ubuntu-latest, qt5, 3.10)	2m 33s
build (macos-latest, qt5, 3.10)	3m 6s
build (macos-latest, qt6, 3.12)	3m 27s
build (macos-latest, qt6, pypy-3.11)	4m 44s
build (windows-latest, qt6, 3.11)	4m 50s
build (macos-latest, qt6, 3.11)	3m 8s
build (macos-latest, qt6, 3.13)	2m 46s
build (macos-latest, qt5, pypy-3.11)	5m 33s
Install from SDist and Test	2m 27s
coverage	0s
	1h 46m 0s

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