Remove redundant translations

[IanDelMar]

Description

This PR

• deprecates 2 redundant translations: __( '1 Comment', 'understrap' ) and __( '% Comments', 'understrap' ).
• adds screen reader text to one string: __( 'Leave a comment<span class="screen-reader-text"> on %s</span>', 'understrap' ).
• updates pot, po and mo files.

Motivation and Context

WP uses the exact same string and provides a translation with better accessibility. See https://github.com/WordPress/WordPress/blob/2f1cac50d34ea42286c89bed28c51ba0b81c17ca/wp-includes/comment-template.php#L1579-L1588. For accessibility reasons we should add a screen reader text to __( 'Leave a comment', 'understrap' ) as well.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I pulled my branch from develop.
• I am submitting my pull request to develop.
• I have resolved any conflicts merging this pull request would create.
• I have checked that there aren't other open Pull Requests for the same update/change.
• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• (Optional) My change requires a change to the documentation.
• (Optional) I have updated the documentation accordingly.
• (Optional) My change requires a change to the translations.
• (Optional) I have updated the translations accordingly.
• composer cs:check has passed locally.
• composer lint:php has passed locally.
• I have read the CONTRIBUTING document.

Further comments

For the part with the screen reader text I used translation from WP 6.0.1 for the string "No Comments on %s". See here for Spanish. I also checked the "Leave a comment" part for consistency here.

[IanDelMar]

For discussion:
I think we should also drop the "leave a comment". WP uses "No Comments on %s" if there are no comments. Which makes sense:

• Otherwise you don't see any information on the number of existing comments if there are no comments. If there are comments it displays the number of comments and not "leave a comment".
• Understrap uses the_excerpt(). Why would you want to "leave a comment" on a post you haven't even read at the time you see "leave a comment"?
• If it does make sense to have "leave a comment" then it should be displayed as well if there is a non-zero number of comments.

Any other thoughts on this? @bacoords ?