Remove deprecated `enableExperimentalViewRenderer` replay option in v9

## Summary

The `MobileReplayOptions.enableExperimentalViewRenderer` option was deprecated in favor of `enableViewRendererV2` in #4815 (2025-05). A compat shim in `mobileReplayIntegration` copies the old value to `enableViewRendererV2` when the new option is unset.

Per the [SDK Deprecation Lifecycle Standard](https://develop.sentry.dev/sdk/), this should be removed in the next major (v9).

## Action for v9

In `packages/core/src/js/replay/mobilereplay.ts`:
- Remove the `enableExperimentalViewRenderer` type definition (`MobileReplayOptions`, ~line 77).
- Remove it from `defaultOptions` (~line 253).
- Remove the compat shim that maps it onto `enableViewRendererV2` (~lines 270-271).
- Update/adjust any related tests.

## References

- Deprecated in #4815 (`ref(session-replay): iOS: Use enableViewRendererV2 instead of the deprecated ...`)
- Replacement: `enableViewRendererV2`
- Sibling v9 removal task: #5882
- [SDK Deprecation Lifecycle Standard](https://develop.sentry.dev/sdk/)

Start in packages/core/src/js/replay/mobilereplay.ts, checking the MobileReplayOptions type, defaultOptions, and mobileReplayIntegration compatibility shim identified in the issue. Then locate related tests and adjust them for the v9 behavior. Done means the deprecated option and mapping are removed, enableViewRendererV2 remains supported, and the related tests pass.

Written by the indexing model from the issue text.