[readme] remove `avn` from readme #1499

Job	Run time
shellcheck_matrix (bash, nvm.sh)	32s
shellcheck_matrix (sh, nvm.sh)	39s
shellcheck_matrix (dash, nvm.sh)	32s
shellcheck_matrix (ksh, nvm.sh)	32s
shellcheck_matrix (bash, install.sh)	25s
shellcheck_matrix (bash, bash_completion)	26s
shellcheck_matrix (bash, nvm-exec)	15s
shellcheck	1s
	3m 22s

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