Remove redundant copy constructor for NGPhysicalConstraintSpace

The existing NGPhysicalConstraintSpace's copy constructor doesn't copy container_size_. This causes some bugs.
C++ compiler provides a copy constructor by default. Lets remove the redundant one.

BUG=635619

Review-Url: https://codereview.chromium.org/2363743006
Cr-Commit-Position: refs/heads/master@{#422306}
2 files changed