fix(v7): remove Rust compiler page and use alpha in upgrade command

[ArmandPhilippot]

Description (required)

• Updates the upgrade guide to use the alpha tag in the upgrade command
• Removes the Rust compiler from experimental flags

Related issues & labels (optional)

• Suggested label: v7

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Tracked Files

File	Note
en/guides/upgrade-to/v7.mdx	Localization changed, will be marked as complete.
en/reference/experimental-flags/rust-compiler.mdx	Source removed, will stop being tracked.
es/reference/experimental-flags/rust-compiler.mdx	Localization removed, will be marked as missing.
fr/reference/experimental-flags/rust-compiler.mdx	Localization removed, will be marked as missing.
ja/reference/experimental-flags/rust-compiler.mdx	Localization removed, will be marked as missing.
ko/reference/experimental-flags/rust-compiler.mdx	Localization removed, will be marked as missing.

Warnings reference

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🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[delucis]

Thanks for cleaning those pages up @ArmandPhilippot!