Twenty Fifteen: Use default comments_popup_link()

[pavelevap]

Function comments_popup_link() now supports plural function _n(), see #26553.

Could we use it for Twenty Fifteen? See attached patch.

I am not sure about backward compatibility, but it should not be a problem?

We can fix missing plural form in Twenty Fifteen and also remove some not needed strings (and also add screen reader HTML).

[SergeyBiryukov]

'Leave a comment' should probably not be removed, the default string is 'No Comments'.

Or we could change the default string for zero comments to 'Leave a comment'.

[pavelevap]

Yes, I would vote for Leave a comment directly in comments_popup_link().

This function should be generally usable in themes and Twenty Fifteen could encourage it.

There is no need for special theme strings and localization when we have it in core with screen readers HTML.

It could be also applied to Twenty Fourteen, I guess...

[obenland]

In 33003:

Twenty Fifteen: Use default strings for comments link.

Also adds context for screen readers, like in default strings.

Props pavelevap for initial patch.
Fixes #32001.

[pavelevap]

Textdomain twentyfifteen is missing?

Should not be string "Leave a comment" direct part of comments_popup_link() function as a better choice?

[obenland]

In 33005:

Twenty Fifteen: Add missing textdomain.

Props pavelevap.
See #32001.