Solely use raw X.509 name data references including SEQUENCE header

So far, the CRT frame structure `mbedtls_x509_crt_frame` used
as `issuer_raw` and `subject_raw` the _content_ of the ASN.1
name structure for issuer resp. subject. This was in contrast
to the fields `issuer_raw` and `subject_raw` from the legacy
`mbedtls_x509_crt` structure, and caused some information
duplication by having both variants `xxx_no_hdr` and `xxx_with_hdr`
in `mbedtls_x509_crt` and `mbedtls_x509_crt_frame`.

This commit removes this mismatch by solely using the legacy
form of `issuer_raw` and `subject_raw`, i.e. those _including_
the ASN.1 name header.
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 535807e..f404f89 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -216,7 +216,7 @@
                                    )
 {
     int ret;
-    size_t len = 0;
+    size_t len;
     mbedtls_asn1_named_data *names = NULL;
     mbedtls_x509_name parsed, *parsed_cur, *parsed_prv;
     unsigned char buf[1024], out[1024], *c;
@@ -234,10 +234,9 @@
 
     ret = mbedtls_x509_write_names( &c, buf, names );
     TEST_ASSERT( ret > 0 );
+    len = (size_t) ret;
 
-    TEST_ASSERT( mbedtls_asn1_get_tag( &c, buf + sizeof( buf ), &len,
-                        MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) == 0 );
-    TEST_ASSERT( mbedtls_x509_get_name( &c, buf + sizeof( buf ), &parsed ) == 0 );
+    TEST_ASSERT( mbedtls_x509_get_name( c, len, &parsed ) == 0 );
 
     ret = mbedtls_x509_dn_gets( (char *) out, sizeof( out ), &parsed );
     TEST_ASSERT( ret > 0 );