Remove long-obsolete `is_blocklisted_fn` mechanism. #411

Job	Run time
Lint	5m 56s
cargo-deny	1m 16s
Test (macOS-latest, x86_64-apple-darwin)	15m 17s
Test (windows-2022, x86_64-pc-windows-msvc)	26m 51s
Test (ubuntu-24.04, x86_64-unknown-linux-gnu)	15m 38s
Test (ubuntu-24.04, aarch64-linux-android, x86_64-unknown-linux-gnu)	7m 56s
test_success	2s
	1h 12m 56s

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