Remove the 2 QualType references to method UsualArithmeticConversions. Last week, I added these
to quickly fix a regression. Avoiding them entirely is a much cleaner solution. Clients of 
UsualArithmeticConversions should simply call getType() on the expression to get the
converted type. In practice, only a small number of routines care about this.

llvm-svn: 39934