tools: temporarily unset LD_LIBRARY_PATH when generating ssh key #19081

Job	Run time
dashboard	2m 12s
build	3m 59s
aux	3m 57s
race_dashboard	2m 52s
arch (presubmit_arch_openbsd)	3m 54s
race	9m 14s
arch (presubmit_arch_netbsd)	3m 33s
arch (presubmit_arch_freebsd)	6m 34s
arch (presubmit_arch_windows)	3m 38s
old	7m 18s
arch (presubmit_arch_darwin)	3m 49s
arch (presubmit_arch_linux)	10m 43s
arch (presubmit_arch_executor)	2m 54s
gvisor	3m 55s
	1h 8m 32s

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