Camera: Fix a crash in removeCamera()

mCameraInfoMap is a KeyedVector, we should use .valueFor() instead of
operator[] to get the value from a key.

Bug: 118364955
Bug: 118359878
Bug: 77833131
Test: Plug and unplug the external camera 10+ times.
Change-Id: Ibf48e5a78b16bdeba08b02242379eaf571fc76cb