Reviewed by Adam Barth.

        Remove LegacyDefaultOptionalArguments flag from IDL files where it would not change behavior
        https://bugs.webkit.org/show_bug.cgi?id=62904

        After bug 62750, there are many IDL files that contain the new
        LegacyDefaultOptionalArguments flag that don't actually need it.
        Some examples:

            - the IDL file contains no functions
            - the IDL file contains only functions with no arguments
            - the IDL file contains functions, *all* of which use the
              [RequiresAllArguments=raise] extended attribute

        This patch simplifies such IDL files by removing the
        LegacyDefaultOptionalArguments flag and (if needed) removing the
        [RequiresAllArguments=raise] extended attribute from each function
        declaration. This patch does not make any required arguments optional
        or any optional arguments required. It changes no behavior at all.

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