Use EVP_PKEY_bits in SimplePathBuilderDelegate

No need to dip out of EVP for this one.

Change-Id: Ide03d28edd5316addbb9051d527fec23ace259ba
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/81660
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

pki/simple_path_builder_delegate.cc

diff --git a/pki/simple_path_builder_delegate.cc b/pki/simple_path_builder_delegate.cc
index 7870611..a3b5205 100644
--- a/pki/simple_path_builder_delegate.cc
+++ b/pki/simple_path_builder_delegate.cc
@@ -100,12 +100,7 @@
   int pkey_id = EVP_PKEY_id(public_key);
   if (pkey_id == EVP_PKEY_RSA) {
     // Extract the modulus length from the key.
-    RSA *rsa = EVP_PKEY_get0_RSA(public_key);
-    if (!rsa) {
-      return false;
-    }
-    unsigned int modulus_length_bits = RSA_bits(rsa);
-
+    unsigned int modulus_length_bits = EVP_PKEY_bits(public_key);
     if (modulus_length_bits < min_rsa_modulus_length_bits_) {
       errors->AddWarning(
           kRsaModulusTooSmall,