fix(timeout.go): remove redundant leaked go func in RegisterTimeoutHa…

…ndler (#4004)

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**What type of PR is this?**

Bug fix

**What does this PR do? Why is it needed?**

Fix #4003 

The removed goroutine is redundant and will fail user code tests where
timeout or sigterm do no happen.

IIUC, we only need to register a noop handler for sigterm signal for
bazel to gracefully shutdown in case of a test timeout and
`signal.Notify(c, signal.SIGTERM)` create a strong reference to prevent
`c` from being GCed when `RegisterTimeoutHandler` returns.

**Which issues(s) does this PR fix?**

Fixes #4003

**Other notes for review**

Tested with my own repo tests and a simple time.Sleep ran with
--test_timeout

go/tools/bzltestutil/timeout.go

@@ -39,7 +39,4 @@ func RegisterTimeoutHandler() {
 	// (2): https://github.com/bazelbuild/rules_go/pull/3929
 	c := make(chan os.Signal, 1)
 	signal.Notify(c, syscall.SIGTERM)
-	go func() {
-		<-c
-	}()
 }