SSHD is not yet beta, take out claim

What does this MR do?

Turns out we didn't release that day after all; back out the claims in !80708 (merged) of this software being in beta. It's still alpha.

Let's leave the grammar / style fixes, though.

Related issues

• Related to Move gitlab-sshd to Beta in documentation (!80708 - merged) where I merged too soon.
• Related to Enable gitlab-sshd on gprd (gitlab-com/gl-infra/production#6321 - closed)

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