aot task should not make network calls

`aot` task uses aether to resolve dependencies, with the default of `:retrieve true`. This causes `aot` to talk to maven repos over the network, even when all the deps are already resolved locally.

This violates the "functional pipeline" idea, where one would expect to be able to fully resolve deps in one task, and then have `aot` just do aot. And it is a problem for locked-down environments that e.g. do not use clojars or maybe even want to run aot when not connected to the network

Changing `aot`'s use of aether to `:retrieve false` might be sufficient to fix this, I don't know enough about aether to be sure.