CodegenCleanup: Drop CFLAA pass from codegen cleanup sequence

Since r274197 -polly-position=before-vectorizer caused various LNT failures
for example in SingleSource/Benchmarks/Linpack. These failures seem to only
occur when the CFLAA pass is scheduled in our codegen-cleanup passes, which
suggests that the way we call this AA pass is somehow problematic.  As this pass
is not of high importance, we drop the pass for now to prevent these failures
from happening. At a later point, we might investigate more in-depth why this
specific usage scenario caused correctness issues.

llvm-svn: 274427