rpc-types-eth: rm `PeerCount` #3448

Job	Run time
wasm-wasi	3m 14s
test ubuntu-latest stable --no-default-features	2m 40s
doctest	2m 34s
test ubuntu-latest stable	2m 31s
clippy	1m 28s
test ubuntu-latest stable --all-features	2m 58s
wasm-unknown	2m 18s
test ubuntu-latest nightly --no-default-features	1m 7s
feature-checks	6m 29s
test ubuntu-latest nightly	1m 24s
cfg-check	29s
test ubuntu-latest nightly --all-features	1m 45s
docs	53s
test ubuntu-latest 1.76 --no-default-features	1m 58s
fmt	12s
test ubuntu-latest 1.76	1m 58s
no-std	34s
test windows-latest stable --no-default-features	7m 26s
test windows-latest stable	7m 16s
test windows-latest stable --all-features	8m 5s
test windows-latest nightly --no-default-features	3m 20s
test windows-latest nightly	4m 9s
test windows-latest nightly --all-features	4m 29s
test windows-latest 1.76 --no-default-features	5m 54s
test windows-latest 1.76	4m 19s
	1h 19m 30s

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