Remove commented tests for Bytes::unsplit (#677) #579

Job	Run time
miri	7m 52s
loom	3m 30s
minrust	3m 32s
cross (i686-unknown-linux-gnu)	32s
nightly	4m 27s
cross (armv7-unknown-linux-gnueabihf)	26s
rustfmt	5s
cross (powerpc-unknown-linux-gnu)	29s
stable (ubuntu-latest)	1m 15s
cross (powerpc64-unknown-linux-gnu)	27s
tsan	3m 51s
stable (macos-latest)	1m 59s
cross (wasm32-unknown-unknown)	6s
stable (windows-latest)	2m 16s
Publish Documentation	3m 34s
	34m 21s

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