cmd/release: delete

Delete the empty command after some time passes.

Updates golang/go#40279.

Change-Id: I4064e4ba329d9a3637459816420603813652ebe2
Reviewed-on: https://go-review.googlesource.com/c/build/+/470756
Run-TryBot: Dmitri Shuralyov <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: dmitshur