Don't use tar's -p with -rf, where it makes no sense.

-p only applies to tar invocations that cause extraction, but -rf is
just appending to a tar file.

toybox tar doesn't have -p, and it doesn't seem worth implementing if
this is our only "user".

Test: treehugger
Change-Id: I025c496b04cb57cb31ba81fd516fd40b158bc06b