Remove an assertion that no longer holds. <rdar://problem/16135814>

In r201528, I changed the PGO instrumentation counter for a "do" loop to not
include the fall-through count. That fall-through count is included later, b
it means that this assertion may fail for "do" loops.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202437 91177308-0d34-0410-b5e6-96231b3b80d8