Deprecate the legacy HTTP+SSE transport #3752

Job	Run time
checks / pre-commit	50s
checks / readme-snippets	13s
checks / docs	58s
checks / test (3.10, lowest-direct, windows-latest)	1m 55s
checks / test (3.11, locked, windows-latest)	1m 55s
checks / test (3.14, lowest-direct, windows-latest)	1m 49s
checks / test (3.11, lowest-direct, windows-latest)	1m 51s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.13, locked, ubuntu-latest)	1m 16s
checks / test (3.10, locked, ubuntu-latest)	1m 34s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 24s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 24s
checks / test (3.14, locked, ubuntu-latest)	1m 20s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 25s
checks / test (3.12, locked, windows-latest)	1m 57s
checks / test (3.10, locked, windows-latest)	1m 43s
checks / test (3.13, locked, windows-latest)	1m 56s
checks / test (3.12, lowest-direct, windows-latest)	1m 59s
checks / test (3.12, locked, ubuntu-latest)	1m 41s
checks / test (3.13, lowest-direct, windows-latest)	2m 6s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 32s
checks / test (3.11, locked, ubuntu-latest)	1m 21s
checks / test (3.14, locked, windows-latest)	2m 4s
all-green	4s
	35m 43s

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