Improve alert list spacing

What does this MR do?

Previously text within the table would not ellipsize, meaning that for long alert names the table would scroll off the edge of the page.

This change fixes this by tweaking the spacing.

It also removes the unused end time column, which adds a little extra space.

Issue: #224638 (closed)

Screenshots

Before	After
table_spacing	percent_widths_nowrap

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [n/a] Documentation (if required) Docs MR here: !35406 (merged)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [n/a] Database guides
• [n/a] Separation of EE specific content

Availability and Testing

• [n/a] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [n/a] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [n/a] Label as security and @ mention @gitlab-com/gl-security/appsec
• [n/a] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [n/a] Security reports checked/validated by a reviewer from the AppSec team