Remove redundant reserve call #571

Job	Run time
loom	3m 34s
miri	7m 47s
minrust	3m 32s
cross (i686-unknown-linux-gnu)	33s
cross (armv7-unknown-linux-gnueabihf)	34s
rustfmt	2s
nightly	4m 28s
cross (powerpc-unknown-linux-gnu)	28s
stable (ubuntu-latest)	1m 14s
cross (powerpc64-unknown-linux-gnu)	26s
stable (macos-latest)	3m 18s
cross (wasm32-unknown-unknown)	6s
tsan	3m 49s
stable (windows-latest)	2m 18s
Publish Documentation	3m 30s
	35m 39s

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