openssl: stop using deprecated read_RSAPublicKey

Starting with openssl 3, the PEM_read_bio_RSAPublicKey function is
deprecated.  There is an existing API, PEM_read_PUBKEY which gives a
nicer EVP_PKEY object instead.  Switch to use this.

Tested: Unit tests pass, which call 'verify' and use this code path.

Change-Id: Id3d5cf5f200ae1fcb66329c848f6c3567f7ef3d7
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/image_verify.hpp b/image_verify.hpp
index d909afe..0d04815 100644
--- a/image_verify.hpp
+++ b/image_verify.hpp
@@ -191,7 +191,7 @@
      * @param[in]  - publickey
      * @param[out] - RSA Object.
      */
-    inline RSA* createPublicRSA(const std::filesystem::path& publicKey);
+    inline EVP_PKEY_Ptr createPublicRSA(const std::filesystem::path& publicKey);
 
     /**
      * @brief Memory map the  file