[LICM] Fix NumSunk statistic (NFC)

LICM can sink instructions that have uses inside the loop, as
long as these uses are considered "free". However, if there were
only free uses inside the loop, and no uses outside the loop at
all, the instruction would still count towards the NumSunk
statistic. This resulted in a wild inflation of the NumSunk metric.
After this patch it drops down from 1141787 to 5852 on test-suite O3.