testsuite: remove .gitignore files when populating rootfs

testsuite: remove .gitignore files when populating rootfs

Usually this file is added to keep a directory existing in the
repository but without any real content. In rootfs this can be
problematic if a directory will have all its files inspected. This
happens for kmod_module_get_holders().

Side-note: the 'test-loaded.c' is hit by this problem but doesn't
"notice" because the invalid module returned by get_holders() is not
checked. The modules in its loop are only used to get the name and
generate an output, and NULL was a valid value to generate the name.