With this powershell command you will be to remove a rendering from sitecore item.
$items = Get-ChildItem -Path "master:/sitecore/content/Home" -Recurse
$rendering = Get-Item master: -ID "{6DDA07A9-18D3-47A0-AB74-DF54956DD5F1}"# Plain HTML
$dataSource = "{F65382DD-AD11-411D-A706-CF05C9C5A332}"# if you want to remove with a specific placeholder.
foreach ( $item in $items )
{
$allrenderings = Get-Rendering -Item $item -Rendering $rendering -DataSource $dataSource
foreach ($allrendering in $allrenderings)
{
write-host "Master Item " $item.Name + "Rendering name - " + $allrendering.Datasource + "PlcaeholderName - " + $allrendering.Placeholder
Remove-Rendering -Item $item -Rendering $rendering -DataSource $dataSource -Placeholder $allrendering.Placeholder
#remove web item
$webItem = Get-Item web: -ID $item.ID
if($webItem)
{
write-host "WebItem - " + $webItem.Name
Remove-Rendering -Item $webItem -Rendering $rendering -DataSource $dataSource -Placeholder $allrendering.Placeholder
}
}
}