Removed Diagnostics from sys.ts in order to avoid cyclical build dependency

Specifically, processDiagnosticMessages.ts was dependent on sys.ts, which was dependent on the rest of the compiler, which meant that after merge, you could never compile processDiagnosticMessages.ts.
i would just make it a constant. we do not have other ones now, so no need to use an enum. I would even make it "-2147024809", just give it a name.