cobalt: Remove unused codes under cobalt/shell

[kjyoun]

Clean up the Android shell implementation by removing various unused
methods, constants, and imports across ContentViewRenderView, Shell,
and ShellManager classes. This dead code is no longer necessary for
the Cobalt Android shell's functionality.

go/deadcode

Issue: 413418478

[github-actions]

🤖 Gemini Suggested Commit Message

---

android: Remove unused code from shell

Clean up the Android shell implementation by removing various unused
methods, constants, and imports across ContentViewRenderView, Shell,
and ShellManager classes. This dead code is no longer necessary for
the Cobalt Android shell's functionality.

Bug: 413418478

---

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[gemini-code-assist]

Code Review

This pull request cleans up the codebase by removing several unused methods, constants, and imports across ContentViewRenderView.java, Shell.java, and ShellManager.java. Specifically, it removes unused helper methods like setSurfaceViewBackgroundColor, isInitialized, isDestroyed, isLoading, getWindow, and an overloaded launchShell method, along with their associated unused imports and constants. There are no review comments, so I have no additional feedback to provide.

[borongc]

Not sure about the plan for rebase Cobalt shell, these are mostly the functions from upstream Content shell, if we remove them, it will increase the difficulty while rebasing Cobalt shell.

We should clearly check with browser team to see if there is any plan to rebase Cobalt shell.