`make run-app-verilator` always recompiles SW and always runs "hello_world"

[cousteaulecommandant]

In 0bfac78, Makefile target app got added a dependency on clean-app, so that every time the user types make app it ensures the app is rebuilt. In 90d9c11, Makefile target run-app-sim (now called run-app-verilator) got added a dependency on app, which ensures that the app is compiled when launching the simulation. However, these two changes combined cause the software application to be always deleted and recompiled every time the Verilator simulation is launched via make run-app-verilator.

A side effect of this is that something like make app PROJECT=not_hello_world && make run-app-verilator will run the default hello_world application instead of running not_hello_world as requested, since the second command will implicitly call make app without the PROJECT=not_hello_world argument. (This can be solved by adding PROJECT=not_hello_world to the second command as well.)

Another side effect is that the simulation takes longer to start because the app needs to be recompiled every time.