Fix overly verbose aria-label in Social Link block

[0aveRyan]

Description

Fixes #20665.

This simplifies the a11y-compatibility added to the Social Link block, removes a confusing translatable string and provides an improved experience for screen reader users.

Screen readers announce anchors as links, so having "Link to" was redundant.

How has this been tested?

• I've navigated a document containing Social Link blocks using VoiceOver on macOS (see screenshots below).

Screenshots

Before:

After:

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

[aduth]

Looks good 👍 Thank you.