sanity.bbclass: recommend using install-buildtools

For old tar version (< 1.28), recommend using
scripts/install-buildtools

Drop check for tar version 1.24. Dubious extra value.

Signed-off-by: Tim Orling <timothy.t.orling@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>