contrib/google.golang.org/grpc: fix flaky tests by removing arbitrary sleeps

[Julio-Guerra]

What does this PR do?

Remove arbitrary calls to time.Sleep.
The test timeout will be enough to gate their exec time if they happen to fail.

Motivation

gRPC tests are extremely flaky on qemu arm64.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[nsrip-dd]

The test timeout will be enough to gate their exec time if they happen to fail.

As a bonus, if the whole test suite times out, you get a stack dump for all the goroutines. So if something was actually stuck the whole time you'll see it.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-02-28 16:47:39

Comparing candidate commit df52b39 in PR branch julio.guerra/remove-grpc-test-flakiness with baseline commit 8373eb9 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 39 metrics, 2 unstable metrics.