chore: Remove Codecov AI code and assets

Complete cleanup of Codecov AI feature following the UI hiding in the
previous PR.

Changes:
- Remove CodecovAIPage component and all sub-components
- Remove codecovAI GraphQL hooks and services
- Remove codecovAI assets (PR review and test gen example images)
- Remove GH_APP_AI config

This is part 2 of the Codecov AI deprecation.
Closes CCMRG-2033

Author: drazisil-codecov

src/assets/codecovAI/pr-review-example-dark-mode.png

@@ -11,7 +11,6 @@ const defaultConfig = {
   SENTRY_SESSION_SAMPLE_RATE: 0.1,
   SENTRY_ERROR_SAMPLE_RATE: 1.0,
   GH_APP: DEFAULT_GH_APP,
-  GH_APP_AI: 'codecov-ai',
   SUNBURST_ENABLED: true,
   DISPLAY_SELF_HOSTED_EXPIRATION_BANNER: true,
 }