[APFloat] Removed out of date comment from isNormal().

I already finished the isIEEENormal => isNormal transition. So isNormal is now
IEEE-754R compliant.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184687 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed