This reverts commit d2170040.

Reason for revert: It broke all the darwin builders; it's also not
obvious how the weird darwin versions (900, 1000) relate to the > 3.9
requisite, so I'm not sure how to decide about skipping in a robust
way. It's better to revert the check for now.

Fixes #28028

Change-Id: Ibbcb7bf7cd2136e0851ebd097a2bc4dec9f0ee18
Reviewed-on: https://go-review.googlesource.com/c/140217Reviewed-by: Keith Randall <khr@golang.org>