PEM_read_RSA_PUBKEY deprecated since OpenSSL 3.0

[mattc-pstg]

This may actually be a duplicate of issue #337; however the compiler output is different therefore I filed a separate ticket for the issue. They have a mitigation guide on deprecated functions here - https://docs.openssl.org/master/man7/ossl-guide-migration/#deprecated-function-mappings.

Maybe we simply use PEM_read_PUBKEY instead?

   39   CC    lib/crc.c
   39   CC    lib/diag.c
   39   CC    lib/events.c
   39   CC    lib/fabric.c
   39   CC    lib/fw.c
   40   CC    lib/gas_mrpc.c
   40   CC    lib/mfg.c
   40 lib/mfg.c: In function ‘switchtec_read_pubk_file’:
   40 lib/mfg.c:881:9: warning: ‘PEM_read_RSA_PUBKEY’ is deprecated: Since OpenSSL 3.0 [-Wdeprecated-declarations]
   40   881 |         RSAKey = PEM_read_RSA_PUBKEY(pubk_file, NULL, NULL, NULL);
   40       |         ^~~~~~
   40 In file included from lib/mfg.c:65:
   40 /usr/include/openssl/pem.h:449:1: note: declared here
   40   449 | DECLARE_PEM_rw_attr(OSSL_DEPRECATEDIN_3_0, RSA_PUBKEY, RSA)
   40       | ^~~~~~~~~~~~~~~~~~~
   40 lib/mfg.c:884:17: warning: ‘PEM_read_RSAPrivateKey’ is deprecated: Since OpenSSL 3.0 [-Wdeprecated-declarations]
   40   884 |                 RSAKey = PEM_read_RSAPrivateKey(pubk_file, NULL, NULL, NULL);
   40       |                 ^~~~~~
   40 /usr/include/openssl/pem.h:447:1: note: declared here
   40   447 | DECLARE_PEM_rw_cb_attr(OSSL_DEPRECATEDIN_3_0, RSAPrivateKey, RSA)
   40       | ^~~~~~~~~~~~~~~~~~~~~~
   40 lib/mfg.c:889:9: warning: ‘RSA_get0_key’ is deprecated: Since OpenSSL 3.0 [-Wdeprecated-declarations]
   40   889 |         RSA_get0_key(RSAKey, &modulus_bn, &exponent_bn, NULL);
   40       |         ^~~~~~~~~~~~
   40 In file included from /usr/include/openssl/x509.h:36,
   40                  from /usr/include/openssl/pem.h:23:
   40 /usr/include/openssl/rsa.h:217:28: note: declared here
   40   217 | OSSL_DEPRECATEDIN_3_0 void RSA_get0_key(const RSA *r,
   40       |                            ^~~~~~~~~~~~
   40 lib/mfg.c:895:9: warning: ‘RSA_free’ is deprecated: Since OpenSSL 3.0 [-Wdeprecated-declarations]
   40   895 |         RSA_free(RSAKey);
   40       |         ^~~~~~~~
   40 /usr/include/openssl/rsa.h:293:28: note: declared here
   40   293 | OSSL_DEPRECATEDIN_3_0 void RSA_free(RSA *r);
   40       |                            ^~~~~~~~```