Revert "unexpand: use buffered read & improve performance by 34.66% … #19012

Job	Run time
Pre-commit hooks	1m 12s
Style/Python	5s
Style/format (ubuntu-latest, feat_os_unix)	41s
Style/spelling (ubuntu-latest, feat_os_unix)	15s
Style/toml	5s
Style/lint (windows-latest, feat_os_windows)	3m 32s
Style/lint (ubuntu-latest, all, true)	2m 57s
Style/lint (macos-latest, feat_os_macos)	4m 1s
	12m 48s

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