dashboard: clear known issue for iOS builder
dashboard: clear known issue for iOS builder

The work needed to resolve go.dev/issue/49616 looks
to be complete, and the builder is passing reliably.

Updates golang/go#49616.

Change-Id: I90253c7751f97f081496abe90b1e827992afaf6e
Reviewed-on: https://go-review.googlesource.com/c/build/+/369255
Trust: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/build,golang/build,golang/build,golang/build