nanobsd: Add _xxx_remove_extra_dist_files

[senguptaangshuman17_gmail.com]

Summary

Remove debug, lib32, and test files from base.txz if those distributions
were not requested in NANO_DISTRIBUTIONS.

This workaround should be removed once fixed in base.txz.

[jlduran]

tools/tools/nanobsd/_xxx_includes.subr

17

Remember to add the reference:

# https://reviews.freebsd.org/D56597

[senguptaangshuman17_gmail.com]

No code changes in this commit. An earlier commit in the stack (D58931) needed a commit-message reword per review feedback, which required a bottom-up arc diff refresh of every commit above it to keep the stack applying cleanly. That refresh is what reset this revision's accepted status, not a content change.

@jlduran, could you re-accept when you get a chance?