Fix comments around TBSCertificate cache.

We don't actually refresh the cache most of the time, just drop it and
live without it. The distinction isn't really visible by callers, but
make the comments accurate.

Change-Id: I7321695337125ca648ab57667564d9578a6fd549
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/54727
Commit-Queue: Adam Langley <agl@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

crypto/x509/x509_test.cc

@@ -1880,7 +1880,7 @@ static bool SignatureRoundTrips(EVP_MD_CTX *md_ctx, EVP_PKEY *pkey) {
   }
 
   // Re-encode the certificate. X509 objects contain a cached TBSCertificate
-  // encoding and |X509_sign_ctx| should have refreshed that cache.
+  // encoding and |X509_sign_ctx| should have dropped that cache.
   bssl::UniquePtr<X509> copy = ReencodeCertificate(cert.get());
   return copy && X509_verify(copy.get(), pkey);
 }
@@ -2025,7 +2025,7 @@ TEST(X509Test, SignCertificate) {
       EXPECT_TRUE(X509_verify(cert.get(), pkey.get()));
 
       // Re-encode the certificate. X509 objects contain a cached TBSCertificate
-      // encoding and |i2d_re_X509_tbs| should have refreshed that cache.
+      // encoding and |i2d_re_X509_tbs| should have dropped that cache.
       bssl::UniquePtr<X509> copy = ReencodeCertificate(cert.get());
       ASSERT_TRUE(copy);
       EXPECT_TRUE(X509_verify(copy.get(), pkey.get()));
@@ -2115,7 +2115,7 @@ TEST(X509Test, SignCRL) {
       EXPECT_TRUE(X509_CRL_verify(crl.get(), pkey.get()));
 
       // Re-encode the CRL. X509_CRL objects contain a cached TBSCertList
-      // encoding and |i2d_re_X509_tbs| should have refreshed that cache.
+      // encoding and |i2d_re_X509_tbs| should have dropped that cache.
       bssl::UniquePtr<X509_CRL> copy = ReencodeCRL(crl.get());
       ASSERT_TRUE(copy);
       EXPECT_TRUE(X509_CRL_verify(copy.get(), pkey.get()));
@@ -2220,7 +2220,7 @@ TEST(X509Test, SignCSR) {
 
       // Re-encode the CSR. X509_REQ objects contain a cached
       // CertificationRequestInfo encoding and |i2d_re_X509_REQ_tbs| should have
-      // refreshed that cache.
+      // dropped that cache.
       bssl::UniquePtr<X509_REQ> copy = ReencodeCSR(csr.get());
       ASSERT_TRUE(copy);
       EXPECT_TRUE(X509_REQ_verify(copy.get(), pkey.get()));