The bitcode parser contained a number of TODO commments about
removing error recovery once the parser was implemented. This
was based on the fact that (1) pnacl-sz in the browser didn't
need it, and (2) it would be trivial to remove.

The advantage of leaving error recovery in is that multiple errors can
be found at once.

It turns out it isn't so easy to remove, since several methods assume
that recovery can be applied, and hence do not need propagate back up
an (optional) error code. Parsing backs out relatively quickly anyway,
since the code exits between bitcode records anyway.

BUG=None
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1286513002 .