internal/scte35: un-export EventIDCompliance?

[ollytom]

For every test case, Segmentation.EventIDCompliance (or anywhere else a so-called event ID field is) the value is always true. But this isn't really specified in plain language in the specs. It looks like it should be calculated from the associated event ID at encode/decode time.

Arguably we don't really need to have the field, exported or not, in the struct. Relevant structures are:

• Event
• Insert
• SegmentationDescriptor