python-mako: rm -df -> rmdir

The old rm (e.g., Ubuntu 12.04's) doesn't has -d option, use rmdir to
make it work. BTW., the "-f" option in rm -df doesn't make any sense.

(From OE-Core rev: 0a78e2051e6e735e3a47a8d46d150f5e62ba505c)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/python/python-mako_1.0.4.bb

@@ -13,5 +13,5 @@ BBCLASSEXTEND = "native nativesdk"
 # The same utility is packaged in python3-mako, so it would conflict
 do_install_append() {
     rm -f ${D}${bindir}/mako-render
-    rm -df ${D}${bindir}
+    rmdir ${D}${bindir}
 }