ell: fix cross compilation

The current fix-dbus-tests.patch uses automake and pkgconfig to figure
out the path of dbus-daemon. This fails when cross-compiling, as
tests aren't run (and checkInputs) not available.

Instead of doing this, we can simply teach the tests to pick up
dbus-daemon from $PATH. This was also sent upstream in
https://lists.01.org/hyperkitty/list/ell@lists.01.org/thread/SQEZAIS2LZXSXGTXOW3GTAM5ZPXRLTN4/.