[NIch]

Как то так

procedure TForm1.Button1Click(Sender: TObject);
var
i : word;
s : string;
begin
s := 'kdfklljk';
for i := 0 to Memo1.Lines.Count-1 do
if Memo1.Lines.Strings[i] = s then
Memo1.Lines.Delete(i);
end;