Allow RSACryptoServiceProvider.SignHash to work with SHA-2 family

Allow RSACryptoServiceProvider.SignHash to work with SHA-2 family

* System.Security.Cryptography/CryptoConfig.cs: Add OID for RIPEMD160
* System.Security.Cryptography/RSACryptoServiceProvider.cs: Update
GetHashNameFromOID to include SHA2-family OIDs. Remove historical
comments about 1.x FX behavior.

* Test/System.Security.Cryptography/CryptoConfigTest.cs: Add test cases
wrt RIPEMD160 OID
* Test/System.Security.Cryptography/RSACryptoServiceProviderTest.cs: Add
test case for SignHash with all FX-provided hash implementations (all
working except RIPEMD160). Remove some NET_2_0/NET_1_1 defines.
* Test/System.Security.Cryptography/RSAPKCS1SignatureFormatterTest.cs:
Remove hacks that were needed for running the tests under FX 1.x. Remove
some NET_2_0/NET_1_1 defines.