Customizer Preview iframe: remove the html loading title attribute

[afercia]

Noticed while testing the Customizer. Sometimes a "Loading ..." title attribute gets added to the html element, for example when checking a Menu Location checkbox:

I'd say it's hardly noticeable and wondering if really useful. If the intent is to show a loading indicator, there are probably better ways to do it. Considering also #24766 would probably make sense to remove this and clean up a bit.

[mehulkaklotar]

Removed html title attribute update on loading and preview.

[mehulkaklotar]

Do we need to remove the localized variable?

'l10n' => array(
    'loading'  => __( 'Loading ...' ),
),

[afercia]

Replying to mehulkaklotar:

Do we need to remove the localized variable?

Yes, if it's not used anywhere else :) Sorry, haven't had time to check.

[mehulkaklotar]

localized variable removed

[afercia]

Refreshed patch after recent changes.

[afercia]

As @ocean90 pointed out, it would be nice to use wp.a11y.speak() to give screen reader users some audible feedback while loading the preview. Changing type to "bug" and moving it into 4.4.

[afercia]

Looked a bit into this, I think it would be possible to dispatch a "speak" message from api.Previewer.refresh() but there's always the chance it will be overridden by other messages, for example when moving down/up a widget, etc. I'd rather keep it simple and stick to the original ticket goal.

[afercia]

In 35391:

Customizer: remove the title attribute from the Preview html element while loading.

Props mehulkaklotar.

Fixes #33250.