make v2 default mode for inline chat (#313184)

* remove old inline chat from extension

* refactor: remove deprecated inline chat V2 configuration and related checks

Co-authored-by: Copilot <copilot@github.com>

* refactor: update context keys for inline chat and clean up unused variables

* address copilot review: fix typo and rename forInlineAndInlineChatIntent

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Co-authored-by: Copilot <copilot@github.com>