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This matches the gn name and is less confusing with use_openssl and
use_openssl_certs both existing. The preprocessor flag will follow
in another CL. 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.

BUG=462040
TBR=wez@chromium.org

Review URL: https://codereview.chromium.org/1085923002

Cr-Commit-Position: refs/heads/master@{#325541}