doc/1.17: fix two dead rfc links

[ferrmin]

Updates golang#44513

Change-Id: Ia0c6b48bde2719f3a99cb216b6166d82159198d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/336930
Trust: Alberto Donizetti [email protected]
Reviewed-by: Ian Lance Taylor [email protected]

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