From `BUILDING.md`, `make moby-cli-link` causes `No rule to make target` error

Location: https://github.com/docker/compose-ecs/blob/main/BUILDING.md#:~:text=help%20with%20this%3A-,make%20moby%2Dcli%2Dlink,-This%20will%20create

```
make moby-cli-link
make: *** No rule to make target 'moby-cli-link'.  Stop.
```

Running just `make` works.

Solutions:
* Remove it from the doc.
* Add the build target to the makefile.