Trim string from the end of a string in .NET - why is this missing?

EDIT - wrapped up into a handy extension method:

public static string TrimEnd(this string source, string value)
{
    if (!source.EndsWith(value))
        return source;

    return source.Remove(source.LastIndexOf(value));
}

so you can just do s = s.TrimEnd("DEF");

TrimEnd() (and the other trim methods) accept characters to be trimmed, but not strings. If you really want a version that can trim whole strings then you could create an extension method. For example...

public static string TrimEnd(this string input, string suffixToRemove, StringComparison comparisonType = StringComparison.CurrentCulture)
{
    if (suffixToRemove != null && input.EndsWith(suffixToRemove, comparisonType)) 
    {
        return input.Substring(0, input.Length - suffixToRemove.Length);
    }

    return input;
}

This can then be called just like the built in methods.

I knocked up this quick extension method.

Not positive it works (I can't test it right now), but the theory is sound.

    public static string RemoveLast(this string source, string value)
    {
        int index = source.LastIndexOf(value);
        return index != -1 ? source.Remove(index, value.Length) : source;
    }

Using Daniel's code and wrapping it in a while rather than a straight if gives functionality more akin to the Microsoft Trim function:

public static string TrimEnd(this string input, string suffixToRemove)
{
    while (input != null && suffixToRemove != null && input.EndsWith(suffixToRemove))
    {
        input = input.Substring(0, input.Length - suffixToRemove.Length);
    }
    return input;
}