fix(reaper): remove termSignal override

[buraindo]

What does this PR do?

Fixes termSignal variable override which led to goroutine leak in reaper.

Why is it important?

Without this change certain scenarios would lead to goroutine leak.

Related issues

• Closes [Bug]: goroutine leaks in reaper #3260

How to test this PR

Use a test from #3260:

func TestContainersFail(t *testing.T) {
	defer goleak.VerifyNone(t)

	net, err := network.New(t.Context())
	require.NoError(t, err)

	req := testcontainers.ContainerRequest{
		Image:        "redis:latest",
		ExposedPorts: []string{"6379/tcp"},
		WaitingFor:   wait.ForLog("Ready to accept connections"),
		Networks:     []string{net.Name},
	}
	redisC, err := testcontainers.GenericContainer(t.Context(), testcontainers.GenericContainerRequest{
		ContainerRequest: req,
		Started:          true,
	})
	require.NoError(t, err)
	require.NoError(t, testcontainers.TerminateContainer(redisC))
	require.NoError(t, net.Remove(t.Context()))
}

I can also commit this test to the PR, if I am allowed to add goleak dependency to go.mod.

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[mdelapenya]

I was able to reproduce the leak with the provided test case, so thank you very much for detecting and resolving it.

LGTM, thanks!