main.star: remove known issue for linux-ppc64le_power{9,10} builders

They've connected and started running.
See https://ci.chromium.org/b/8751480727881152721
and https://ci.chromium.org/b/8751480728981608321.

For golang/go#66667.
For golang/go#64660.

Change-Id: I96d1a5ebc7513a0aa66bb3467d46f1cb0325b79d
Reviewed-on: https://go-review.googlesource.com/c/build/+/576917
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: dmitshur