make should traverse all path subcomponents of CONFIGURED_APPS about nuttx-apps

[patacongo]

* recurse every subdirectory in `apps/`: slow and wasteful, not really necessary (brute force approach)

originally, the system cleaned only CONFIGURED_APPS. But that stranded object files after a reconfiguration. In that case, object files in directories no longer in the configuration would be stranded forever. Cleaning everything eliminated that problem.

[protobits]

But now it is not cleaning everything, it is guided by the placeholder files and as I mentioned it is not enough.
The brute force would really clear everything but that is only reasonable if one always does make -j8 at least.

[xiaoxiang781216]

List the related patch:
#395
apache/nuttx#1843

[protobits]

Nevermind, I found that this was due to a "dirty" workspace: I was missing a .kconfig and since this is only regenerated after distclean it would not include this app to the cleandirs. I will close this since it is not actually a bug, but I think we should revisit this in the future, right now the build system is extremely complex and hard to maintain.