Some post-mortem metadata constants that are not offsets to objects'
properties were incorrectly defined in the accessors table. This change
fixes it by moving them from the accessors table to the constants table.

More background is available at
https://github.com/nodejs/post-mortem/issues/27.

R=danno@chromium.org,bmeurer@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2051563003
Cr-Commit-Position: refs/heads/master@{#36878}