zeroize: remove explicit passing of the docsrs configuration flag (#1… #1308

Job	Run time
linux (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	26s
linux (x86_64-unknown-linux-gnu, 1.85.0)	16s
windows (x86_64-pc-windows-gnu, stable)	37s
linux (x86_64-unknown-linux-gnu, stable)	16s
linux (i686-unknown-linux-gnu, 1.85.0, sudo apt update && sudo apt install gcc-multilib)	27s
windows (x86_64-pc-windows-gnu, 1.85.0)	40s
macos (1.85.0)	19s
cross (aarch64-unknown-linux-gnu, 1.85.0)	40s
cross (aarch64-unknown-linux-gnu, stable)	26s
macos (stable)	26s
minimal-versions / minimal-versions	20s
build-only	19s
	5m 12s

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