TINYDOC-3668: Simplify the Using Comments page, remove the screenshots, and correct the steps against source.

[kemister85]

Ticket: TINYDOC-3668

Site: Staging branch

Changes:

• comments-using-comments.adoc: removed the screenshots so every step is in text, corrected the steps against the plugin source (highlight description, the resolve confirmation dialog and what resolving does in each mode, the mentions placeholder, Shift+Enter, dialog wording), shortened the steps, and linked to the Comments interactive example.
• Deleted the 17 screenshot images that are no longer referenced.

Note: the link to the interactive example uses the #comments-live-demo anchor added in #4400 (TINYDOC-3652), so #4400 should merge first.

Pre-checks:

• Branch is correctly prefixed:
• Files removed have been deleted, not just excluded from the build (if applicable).
• Build passes without console errors, warnings, or issues.

Review:

• Documentation Team Lead has reviewed.