Cody Ignore: deprecated (#5537)

RE
https://linear.app/sourcegraph/issue/CODY-3665/kill-support-for-codyignore

This PR removes the cody ignore feature that was previously hidden
behind a feature flag intended for internal dev use.

This feature has been replaced by Context Filter, a feature currently
available for Enterprise users.

## Test plan

<!-- Required. See
https://docs-legacy.sourcegraph.com/dev/background-information/testing_principles.
-->

Green CI - all current features and tests should not be affected by the
removal of this feature.

## Changelog

<!-- OPTIONAL; info at
https://www.notion.so/sourcegraph/Writing-a-changelog-entry-dd997f411d524caabf0d8d38a24a878c
-->

Deprecate Cody Ignore.

.gitignore

@@ -16,3 +16,4 @@ playwright-report
 test-results
 .vscode-test/
 .envrc
+agent/bindings/kotlin/lib/bin/