$linesToRemove = @(
    '<script src="../../../Scripts/AC_ActiveX.js" type="text/javascript"></script>',
    '<script src="../../../Scripts/AC_RunActiveContent.js" type="text/javascript"></script>',
    '<script src="../../../Scripts/swfobject_modified.js" type="text/javascript"></script>'
)

Get-ChildItem -Path . -Filter "*.php" | ForEach-Object {
    $file = $_.FullName
    $content = Get-Content $file | Where-Object { $_ -notin $linesToRemove }
    $content | Set-Content $file -Encoding UTF8
}