ibus regression

USN-4134-1 fixed a vulnerability in IBus. The security fix introduced a
regression when being used with Qt applications. This update reverts the
security fix pending further investigation.

Original advisory details:

Simon McVittie discovered that IBus did not enforce appropriate access
controls on its private D-Bus socket. A local unprivileged user who
discovers the IBus socket address of another user could exploit this to
capture the key strokes of the other user.