Deleting a tooltip via the trash icon also deletes the underlying word

When clicking the trash/delete icon in the tooltip editing wysiwyg, the
module not only removes the tooltip formatting but also deletes the word
the tooltip was attached to. The selected text disappears entirely instead
of being left as plain text.

1. Enable the CKEditor Tooltips button on a text format.
2. Select a word in the editor, click the tooltip icon, fill in
Title/Content, save.
3. Click into the tooltip text, click the delete (trash) icon.
4. Expected after fix: the word remains in the editor as plain text,
with no tooltip formatting.
5. Before fix (bug):: the word disappears entirely.
6. Repeat with a tooltip created on a collapsed selection (no text
selected, placeholder "i" used) and confirm the placeholder character
behaves consistently with the team's expectations (see edge case above).

the delete (trash) button removes the tooltip's wrapped text entirely
instead of just stripping the tooltip formatting. Root cause:
`CkeditorTooltipUI._deleteTooltip()` calls `writer.remove(range)`, which
deletes model content, rather than `writer.removeAttribute()`, which would
only clear the tooltip-related attributes and preserve the text. Patch
attached.