USE_NSS is confusing because it's not actually the analog of USE_OPENSSL; it's
the analog to USE_OPENSSL_CERTS. This is in preparation for the chimera build
which will set USE_OPENSSL and USE_NSS(_CERTS).

This CL was partially done automatically by the following command:

  git grep -l USE_NSS | xargs sed -i -e 's/defined(USE_NSS)/defined(USE_NSS_CERTS)/'

The remaining were caught by the following command and fixed manually:

  git grep 'USE_NSS\([^_]\|$\)'

Finally, the following command verified nothing in a separate repository was
sensitive to this change:

  find . -name '*.cc' -o -name '*.h' | xargs grep 'USE_NSS\([^_]\|$\)'

For now, the old name is still defined, but not used within Chromium.

A follow-up CL will remove deprecated use_nss and USE_NSS #defines
together which will then cause downstream churn. Though from a grep
of known downstreams, the churn seems to be fairly minimal. The
removal is split from this CL so that, if we need to revert, the
CL to revert is small.

TBR=pneubeck@chromium.org
BUG=462040

Review URL: https://codereview.chromium.org/1082123003

Cr-Commit-Position: refs/heads/master@{#325710}