[PECOFF] Remove unnecessary assertion.
[PECOFF] Remove unnecessary assertion.

Bugs that would be caught by this assertion would also be caught by
RoundTripYAMLPass test. We've enabled the pass for PECOFF, so we can remove
this.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@193886 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld