polarssl: drop use of 1.2 compatibility header.

API has changed since version 1.3. A compatibility header has been created
to ensure forward compatibility for code using old API:
 * x509 certificate structure has been renamed to from x509_cert to
   x509_crt
 * new dedicated setter for RSA certificates ssl_set_own_cert_rsa,
   ssl_set_own_cert is for generic keys
 * ssl_default_ciphersuites has been replaced by function
   ssl_list_ciphersuites()

This patch drops the use of the compatibly header.
polarssl: break compatibility with version older than 1.3.

Remove all #ifdef/else/endif macros that ensure compatibility with polarssl
version previous than 1.3.