Remove Windows XP SHA-256 and ECDSA logic.

net/data/ssl/certificates/README

 This directory contains various certificates for use with SSL-related
 unit tests.
 
 ===== Real-world certificates that need manual updating
 - google.binary.p7b
 - google.chain.pem
 - google.pem_cert.p7b
 - google.pem_pkcs7.p7b
 - google.pkcs7.p7b
 - google.single.der
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 - name_constraint_bad.pem
 - name_constraint_good.pem
     Two certificates used to test the built-in ability to restrict a root to
     a particular namespace.
 
 - bad_validity.pem
     A certificate and private key only valid on 0001-01-01. Windows refuses to
     parse this certificate.
 
-- sha256.pem: Used to test the handling of SHA-256 certs on Windows.
-
 - spdy_pooling.pem : Used to test the handling of spdy IP connection pooling
 
 - subjectAltName_sanity_check.pem : Used to test the handling of various types
      within the subjectAltName extension of a certificate.
 
 - punycodetest.pem : A test self-signed server certificate with punycode name.
      The common name is "xn--wgv71a119e.com" (日本語.com)
 
 - sha1_2016.pem
     Used to test the handling of SHA1 certificates expiring in 2016.
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 ===== From net/data/ssl/scripts/generate-aia-certs.sh
 - aia-cert.pem
 - aia-intermediate.der
 - aia-root.pem
      A certificate chain which we use to ensure AIA fetching works correctly
      when using NSS to verify certificates (which uses our HTTP stack).
      aia-cert.pem has a caIssuers that points to "aia-test.invalid" as the URL
      containing the intermediate, which can be served via a URLRequestFilter.
      aia-intermediate.der is stored in DER form for convenience, since that is
      the form expected of certificates discovered via AIA.