LU-15785 tests: do not detect versions for RPC_MODE mode

LU-15785 tests: do not detect versions for RPC_MODE mode

lustre_version_code() is called each time when do_rpc_nodes()
is called. It is not needed to detect versions for RPC_MODE mode.

Lustre-change: https://review.whamcloud.com/47144
Lustre-change: e3fcd81ae5f378ac62754a659c7adf0e0b656cf3

Fixes: 8fa23490bb ("LU-1538 tests: standardize test script init - sanity")
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-10914
Change-Id: Ia7645de0a4eedfddf859c80e661ebcb2e45de140
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/55272
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>