Clean up remains of field_pos_list #7515

Job	Run time
Type hints check	29s
Build doc	6m 6s
Code health check	1m 12s
Check SPDX identifiers	6s
CodeQL analysis	2m 18s
ubuntu-latest 3.11 non_root -K scanner	3m 53s
ubuntu-latest 3.10 non_root -K scanner	4m 3s
ubuntu-latest 3.12 root -k scanner	4m 41s
macos-14 3.12 both -K scanner	4m 44s
pyca/cryptography test	24s
ubuntu-latest libpcap 3.12 root -K scanner	4m 42s
ubuntu-latest pypy3.9 root -k scanner	4m 5s
ubuntu-latest pypy3.9 root -K scanner	5m 7s
macos-14 3.12 both -k scanner	1m 21s
ubuntu-latest 3.12 non_root -K scanner	4m 41s
ubuntu-22.04 3.7 non_root -K scanner	4m 17s
ubuntu-latest 3.8 non_root -K scanner	4m 29s
ubuntu-latest 3.9 non_root -K scanner	4m 45s
ubuntu-latest 3.12 root -K scanner	5m 23s
	1h 6m 46s

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