tests: revert testing against prerelease deps on Python 3.9 (#426)

tseaver · web-flow · commit cf9cddbfeb57 · 2021-08-18T16:12:09.000Z
Reverts #415 Consensus from today's meeting is that testing prereleases of third-party dependencies needs to happen outside the normal `presubmit` path.
diff --git a/testing/constraints-3.9.txt b/testing/constraints-3.9.txt
@@ -1,2 +0,0 @@
-# Allow prerelease requirements
---pre

Original file line number	Diff line number	Diff line change
`@@ -1,2 +0,0 @@`
`1`		`-# Allow prerelease requirements`
`2`		`---pre`