docs: remove prompt symbols from shell snippets #6864

Job	Run time
cross-i386	58s
test (ubuntu-20.04, 1.22.x, rootless, -race)	7m 32s
cross-i386 (runc_nodmz)	1m 1s
test (ubuntu-20.04, 1.22.x, rootless)	7m 17s
test (ubuntu-20.04, 1.22.x, -race)	7m 50s
test (ubuntu-20.04, 1.22.x)	6m 55s
test (ubuntu-20.04, 1.23.x, rootless, -race)	7m 42s
test (ubuntu-20.04, 1.23.x, rootless)	7m 4s
test (ubuntu-20.04, 1.23.x, -race)	7m 44s
test (ubuntu-20.04, 1.23.x)	7m 35s
test (ubuntu-20.04, 1.23.x, criu-dev)	8m 1s
test (ubuntu-24.04, 1.22.x, rootless, -race)	9m 40s
test (ubuntu-24.04, 1.22.x, rootless)	9m 6s
test (ubuntu-24.04, 1.22.x, -race)	7m 38s
test (ubuntu-24.04, 1.22.x)	6m 51s
test (ubuntu-24.04, 1.23.x, rootless, -race)	9m 47s
test (ubuntu-24.04, 1.23.x, rootless)	9m 37s
test (ubuntu-24.04, 1.23.x, -race)	8m 3s
test (ubuntu-24.04, 1.23.x)	7m 24s
test (ubuntu-24.04, 1.23.x, runc_nodmz)	7m 24s
test (ubuntu-24.04, 1.23.x, criu-dev)	7m 58s
test (actuated-arm64-6cpu-8gb, 1.23.x, rootless)	11m 40s
test (actuated-arm64-6cpu-8gb, 1.23.x)	7m 50s
all-done	1s
	2h 52m 38s

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