Simplify serialize.h's exception handling

Remove the 'state' and 'exceptmask' from serialize.h's stream implementations,
as well as related methods.

As exceptmask always included 'failbit', and setstate was always called with
bits = failbit, all it did was immediately raise an exception. Get rid of
those variables, and replace the setstate with direct exception throwing
(which also removes some dead code).

As a result, good() is never reached after a failure (there are only 2
calls, one of which is in tests), and can just be replaced by !eof().

fail(), clear(n) and exceptions() are just never called. Delete them.

src/test/alert_tests.cpp

@@ -83,7 +83,7 @@ struct ReadAlerts
         std::vector<unsigned char> vch(alert_tests::alertTests, alert_tests::alertTests + sizeof(alert_tests::alertTests));
         CDataStream stream(vch, SER_DISK, CLIENT_VERSION);
         try {
-            while (stream.good())
+            while (!stream.eof())
             {
                 CAlert alert;
                 stream >> alert;