fix(codecatalyst): simplify InactivityMessage

[justinmk3]

Problem

• The "progress" message tests are flaky because of the complex logic, and sometimes fail:

  1) InactivityMessages
       shows expected messages 5 minutes before shutdown on a 60 minute inactivity timeout:
     AssertionError [ERR_ASSERTION]: Expected 3 messages, but got 2
      at assertMessagesShown (src/testInteg/codecatalyst/devEnv.test.ts:182:20)
      at async Context.<anonymous> (src/testInteg/codecatalyst/devEnv.test.ts:85:9)

• Toolkit has complex logic for showing a "progress" message when the codecatalyst dev env timeout is approaching, followed by different logic for showing the "final" message. This isn't worth the complexity because if the user sees the message, clicking it is zero-cost and will happen immediately, otherwise the user isn't active and won't see any of the messages anyway.
• The non-modal progress message may be hidden if the user enabled vscode's "do not disturb" feature.

Solution

• Remove the non-modal "progress" message. Only show the final, modal message starting 5 min before shutdown. Display it until user clicks it.

Followup to https://taskei.amazon.dev/tasks/IDE-13892

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[justinmk3]

/runintegrationtests