chore(DASH): Remove support for float durations.

We previously supported float duration attributes in DASH
SegmentTemplate, due to an ambiguity in the DASH samples.

The code linked to a DASH IOP issue asking if duration could be a
float or it had to be an int.

That issue has since been closed, with the clarification that
duration attributes must be an unsigned int and the sample was
in violation of the spec.

lib/dash/mpd_utils.js

@@ -282,12 +282,6 @@ shaka.dash.MpdUtils = class {
     const durationStr =
         MpdUtils.inheritAttribute(context, callback, 'duration');
     let segmentDuration = TXml.parsePositiveInt(durationStr || '');
-    const ContentType = shaka.util.ManifestParserUtils.ContentType;
-    // TODO: The specification is not clear, check this once it is resolved:
-    // https://github.com/Dash-Industry-Forum/DASH-IF-IOP/issues/404
-    if (context.representation.contentType == ContentType.IMAGE) {
-      segmentDuration = TXml.parseFloat(durationStr || '');
-    }
     if (segmentDuration) {
       segmentDuration /= timescale;
     }