connecting directly to the ESXi 5.1 host
$HostToPatch="<name>"
$esxcli=Get-Esxcli -server $server
$dellsoftware=$esxcli.software.vib.list() | Where { $_.Name -like "*dell*"}
$dellsoftware | ForEach { $esxcli.software.vib.remove($false,$true,$false,$true,$_.Name)}
$Server=Connect-viserver $HostToPatch -user $HostUser -password $HostPass