developer/api/v1/addons/Remove-AddonInstance.ps1

function Remove-AddonInstance
{
    [CmdletBinding(SupportsShouldProcess)]
    param(
        [Parameter(Mandatory)]
        [string] $AddonAlias,
        [Parameter(Mandatory)]
        [string] $InstanceAlias
    )

    if ($PSCmdlet.ShouldProcess($InstanceAlias))
    {
        return Invoke-Api Delete "/developer/api/v1/addons/$AddonAlias/$InstanceAlias"
    }
}