Remove redundant reserve call #576

Job	Run time
loom	3m 30s
cross (i686-unknown-linux-gnu)	27s
minrust	3m 26s
cross (armv7-unknown-linux-gnueabihf)	33s
miri	7m 50s
cross (powerpc-unknown-linux-gnu)	39s
nightly	4m 33s
cross (powerpc64-unknown-linux-gnu)	31s
rustfmt	5s
stable (ubuntu-latest)	1m 8s
cross (wasm32-unknown-unknown)	15s
tsan	3m 51s
stable (macos-latest)	3m 16s
stable (windows-latest)	2m 15s
Publish Documentation	3m 18s
	35m 37s

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