Remove comparison with TTML2.

[skynavga]

Remove the following text from introduction, which is incomplete and inaccurate:

Simple karaoke content can already be represented using [TTML2] using as an example the following approach:

Example 1 ...

This approach has limitations. The style properties available in [TTML2] cannot represent all the complex effects that may be used in Karaoke. For example, using a continuous animation to fill the text with a color sweep is not possible. Animating a bouncing ball on top of the text to represent the word being sung would not be easy, if at all possible. Additionally, the above syntax does not carry semantics enabling a presentation processor to apply user-specific or implementation-specific karaoke styles.

This is inaccurate because:

• TTML2 permits referring to image/svg+xml content via the <image> element, which can indeed support "continuous animation to fill the text with a color sweep" and also "animating a bouncing ball";
• TTML2 permits the use of embedded or externally referenced fonts that may include SVG images to serve as glyphs, e.g., see OpenType SVG Table, which would also enable "continuous animation to fill the text with a color sweep" and also "animating a bouncing ball";
• TTML permits implementations to apply "user-specific or implementation-specific" processing, including, e.g., the use of implementation specific metadata or global attributes in an implementation specific namespace;