Remove deprecated `shell_streams` and `_parent_header` shims #4162

Job	Run time
Test Minimum Versions	2m 43s
Make SDist	32s
link_check	2m 2s
Test Prereleases	2m 51s
test_docs	47s
Test Lint	1m 2s
check_release	1m 43s
test_without_debugpy (ubuntu-latest, 3.10)	2m 18s
build (ubuntu-latest, qt5, pypy-3.11)	3m 48s
build (ubuntu-latest, qt6, 3.12)	2m 57s
build (windows-latest, qt6, 3.10)	5m 16s
build (ubuntu-latest, qt5, 3.14)	2m 40s
build (ubuntu-latest, qt6, 3.13)	2m 42s
build (ubuntu-latest, qt6, 3.11)	2m 43s
build (macos-latest, qt6, 3.10)	2m 54s
build (windows-latest, qt6, 3.12)	4m 48s
build (windows-latest, qt6, 3.13)	6m 6s
build (macos-latest, qt5, 3.14)	3m 8s
build (windows-latest, qt5, pypy-3.11)	5m 54s
build (macos-latest, qt6, 3.13)	3m 11s
build (ubuntu-latest, qt6, 3.10)	2m 53s
build (windows-latest, qt6, 3.11)	4m 9s
build (ubuntu-latest, qt6, pypy-3.11)	3m 33s
build (windows-latest, qt5, 3.14)	6m 30s
build (ubuntu-latest, qt5, 3.10)	2m 44s
build (windows-latest, qt5, 3.10)	4m 10s
build (macos-latest, qt6, 3.11)	3m 0s
build (windows-latest, qt6, pypy-3.11)	6m 32s
build (macos-latest, qt6, pypy-3.11)	7m 12s
build (macos-latest, qt5, pypy-3.11)	4m 49s
build (macos-latest, qt6, 3.12)	2m 57s
build (macos-latest, qt5, 3.10)	3m 13s
Install from SDist and Test	2m 33s
coverage	9s
	1h 54m 29s

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