docs: trim comments and docs from workspace emptying change (#1403)

Follow-up to https://gitea.com/gitea/runner/commit/79faf5e55df7a3b312fb4888b7405a58e01f567c. Reverts the post-task-script doc change, which is too much detail for that page. Also shortens the `DrainGracePeriod` comment and the other comments that commit added, since the code and log messages already say most of it.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1403
Reviewed-by: bircni <[email protected]>
Co-authored-by: silverwind <[email protected]>

act/container/container_types.go

@@ -25,11 +25,7 @@ import (
 
 var hostOS = runtime.GOOS // replaced in tests
 
-// DrainGracePeriod bounds how long we wait for an output-copy goroutine to
-// finish draining a container's output before returning, so that neither a
-// cancellation (waitForCommand) nor a normal container exit (wait) truncates
-// the tail of the log. It is a safety bound: in the common case the stream
-// reaches EOF and the goroutine returns well before this elapses.
+// DrainGracePeriod caps the wait for container output to drain so the log tail is not truncated
 const DrainGracePeriod = 2 * time.Second
 
 // ExitCodeError reports a non-zero process exit code from a container command.