all.bash: remove stale comment about test parallelism

Change-Id: I583da888e37d4483faa6d4b463b0bceac6374166
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/456458
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

all.bash

@@ -40,8 +40,6 @@ echo "Running: go mod tidy"
 go mod tidy
 
 echo "Running: go test ./..."
-# We use the `-p 1` flag because several tests must be run in serial due to
-# their non-hermetic nature (as they interact with a running Postgres instance).
 go test -count=1 ./...
 
 # This test needs to be run separately since an attempt to use the given flag