RecoverySystem: update comment to reflect signature changes

            // The signature cert matches a trusted key.  Now verify that

            // the digest in the cert matches the actual file data.

            // The verifier in recovery *only* handles SHA1withRSA

            // signatures.  SignApk.java always uses SHA1withRSA, no

            // matter what the cert says to use.  Ignore

            // cert.getSigAlgName(), and instead use whatever

            // algorithm is used by the signature (which should be

            // SHA1withRSA).

            // The verifier in recovery only handles SHA1withRSA and

            // SHA256withRSA signatures.  SignApk chooses which to use

            // based on the signature algorithm of the cert:

            //

            //    "SHA256withRSA" cert -> "SHA256withRSA" signature

            //    "SHA1withRSA" cert   -> "SHA1withRSA" signature

            //    "MD5withRSA" cert    -> "SHA1withRSA" signature (for backwards compatibility)

            //    any other cert       -> SignApk fails

            //

            // Here we ignore whatever the cert says, and instead use

            // whatever algorithm is used by the signature.

            String da = sigInfo.getDigestAlgorithm();

            String dea = sigInfo.getDigestEncryptionAlgorithm();