Remove support for MD2

No part of IKE/IPsec or X.509 uses MD2 anymore, so there really is no
reason to still support it (unlike MD4 that is used in EAP-MSCHAPv2,
MD5 that's used in EAP-MD5, or SHA-1 that's used for e.g. NAT-D hashes).

It caused test vectors to fail on systems where OpenSSL is built with
MD2 support but has it disabled at runtime.

src/libstrongswan/asn1/oid.txt

@@ -94,7 +94,7 @@
             0x01             "PKCS"
               0x01           "PKCS-1"
                 0x01         "rsaEncryption"			OID_RSA_ENCRYPTION
-                0x02         "md2WithRSAEncryption"		OID_MD2_WITH_RSA
+                0x02         "md2WithRSAEncryption"
                 0x04         "md5WithRSAEncryption"		OID_MD5_WITH_RSA
                 0x05         "sha-1WithRSAEncryption"	OID_SHA1_WITH_RSA
                 0x07         "id-RSAES-OAEP"			OID_RSAES_OAEP
@@ -148,7 +148,7 @@
                     0x05     "secretBag"
                     0x06     "safeContentsBag"
             0x02             "digestAlgorithm"
-              0x02           "md2"						OID_MD2
+              0x02           "md2"
               0x05           "md5"						OID_MD5
               0x07           "hmacWithSHA1"				OID_HMAC_SHA1
               0x08           "hmacWithSHA224"			OID_HMAC_SHA224