Trim the migration guide to genuine v1-to-v2 breaking changes #3673

Job	Run time
checks / docs	1m 4s
checks / readme-snippets	15s
checks / pre-commit	59s
checks / test (3.10, lowest-direct, windows-latest)	1m 58s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 16s
checks / test (3.11, locked, windows-latest)	1m 59s
checks / test (3.10, locked, windows-latest)	1m 32s
checks / test (3.11, locked, ubuntu-latest)	1m 25s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.12, locked, ubuntu-latest)	1m 34s
checks / test (3.10, locked, ubuntu-latest)	1m 13s
checks / test (3.12, lowest-direct, windows-latest)	1m 56s
checks / test (3.13, lowest-direct, windows-latest)	2m 1s
checks / test (3.14, lowest-direct, windows-latest)	1m 50s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.11, lowest-direct, windows-latest)	1m 55s
checks / test (3.14, locked, ubuntu-latest)	1m 22s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 30s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 17s
checks / test (3.14, locked, windows-latest)	1m 57s
checks / test (3.13, locked, windows-latest)	1m 49s
checks / test (3.13, locked, ubuntu-latest)	1m 20s
checks / test (3.12, locked, windows-latest)	2m 0s
all-green	2s
	34m 44s

Provide feedback