Remove use_byte_certs buildflag and x509_certificate_nss code.

Bug: 769549
Change-Id: I2b6064bed9a530b46653094e7ddfa201c5b55e8c
Reviewed-on: https://chromium-review.googlesource.com/741551
Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Matt Mueller <mattm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512246}

• chrome/browser/net/profile_network_context_service.cc[diff]
• chrome/browser/net/system_network_context_manager.cc[diff]
• net/BUILD.gn[diff]
• net/cert/cert_verify_proc_unittest.cc[diff]
• net/cert/x509_cert_types.cc[diff]
• net/cert/x509_cert_types.h[diff]
• net/cert/x509_cert_types_unittest.cc[diff]
• net/cert/x509_certificate.h[diff]
• net/cert/x509_certificate_nss.cc[Deleted - diff]
• net/cert/x509_certificate_unittest.cc[diff]
• net/cert/x509_util.cc[diff]
• net/cert/x509_util_nss.cc[diff]
• net/cert/x509_util_nss_unittest.cc[diff]
• net/http/transport_security_state.cc[diff]
• net/ssl/client_cert_store_nss.cc[diff]
• net/ssl/openssl_ssl_util.cc[diff]
• net/third_party/nss/ssl/cmpcert.cc[diff]