[2.x] Fix pools list page's delete button visibility in search filters

[hogan-tech]

Description

This PR fixes a UI bug in the Pools List page where the "Delete" (remove filter) button for search filters was not fully visible. The issue was caused by legacy table cell (td) settings in the template, which became problematic after upgrading the Flask-AppBuilder package. The button was partially hidden, with only its right border visible, making it difficult for users to remove filters.

What was changed:

• Adjusted the table cell settings in pool_list.html to ensure the remove filter button is always fully visible and accessible in the Pools List filter UI.

How to reproduce

1. Go to Admin → Pools in the Airflow UI (Admin tab → Pools button in dropdown).
2. Click the search filter button.
3. Observe that the delete (remove filter) button is not fully visible (only the right border shows).

What you think should happen instead

The delete search filter button should be fully visible and easily clickable.

Related PRs

• Airflow: Add 'Show record' option for variables
• Flask-AppBuilder: fix: filter list UI spacing between elements
• [2.x] Fix delete button visibility in search filters

Additional context

• This issue appeared after upgrading Flask-AppBuilder, which changed some default table rendering behaviors.
• The fix is backward-compatible and only affects the Pools List page.

Screenshots

Before:

After:

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Please review and let me know if further adjustments are needed.