Do not use the CSIM IMSI for mobile operator MNC.

The IMSI on the CSIM application, if present, does not contain
the MNC. We can use it for country detection but not for
operator detection, so don't set the SIM operator based on it.

Bug: 13661632
Change-Id: I49957eba87aa323d7e5894026de6a1e42e47f812