tests: revert testing prerelease deps on Python 3.9 (googleapis#132)

tseaver · web-flow · commit 1be7220f5248 · 2021-08-18T12:04:26.000-04:00
Consensus from today's meeting is that testing against prereleases needs to happen outside the normal presubmit path. Reverts only part of PR googleapis#129.
diff --git a/packages/google-cloud-core/testing/constraints-3.9.txt b/packages/google-cloud-core/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`