Remove deprecated `shell_streams` and `_parent_header` shims #3972

Job	Run time
Test Minimum Versions	2m 38s
test_docs	43s
Test Prereleases	2m 34s
Make SDist	30s
link_check	3m 45s
test_without_debugpy (ubuntu-latest, 3.10)	2m 14s
Test Lint	1m 1s
check_release	1m 44s
build (ubuntu-latest, qt6, 3.12)	2m 39s
build (ubuntu-latest, qt5, pypy-3.11)	3m 39s
build (windows-latest, qt5, 3.14)	4m 49s
build (ubuntu-latest, qt6, pypy-3.11)	3m 15s
build (windows-latest, qt5, pypy-3.11)	6m 52s
build (ubuntu-latest, qt6, 3.13)	2m 36s
build (ubuntu-latest, qt5, 3.10)	2m 35s
build (windows-latest, qt6, 3.11)	4m 17s
build (ubuntu-latest, qt6, 3.11)	2m 36s
build (ubuntu-latest, qt6, 3.10)	2m 47s
build (macos-latest, qt6, pypy-3.11)	5m 2s
build (macos-latest, qt5, pypy-3.11)	4m 33s
build (macos-latest, qt5, 3.14)	2m 20s
build (windows-latest, qt6, 3.13)	3m 56s
build (windows-latest, qt5, 3.10)	7m 52s
build (windows-latest, qt6, 3.12)	4m 34s
build (windows-latest, qt6, pypy-3.11)	6m 22s
build (macos-latest, qt6, 3.12)	3m 18s
build (macos-latest, qt5, 3.10)	2m 43s
build (macos-latest, qt6, 3.11)	3m 6s
build (macos-latest, qt6, 3.10)	3m 11s
build (macos-latest, qt6, 3.13)	2m 32s
build (ubuntu-latest, qt5, 3.14)	2m 31s
build (windows-latest, qt6, 3.10)	4m 6s
Install from SDist and Test	2m 19s
coverage	13s
	1h 49m 52s

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