[Diagnostics] Remove rendering of educational notes to the terminal

We're moving over to a model where we provide direct links to educational notes /
diagnostic group notes whenever relevant. Rendering the Markdown from these
files to the terminal is less relevant with this approach, so remove it from the
compiler.

lib/Frontend/CompilerInvocation.cpp

@@ -2562,7 +2562,6 @@ static bool ParseDiagnosticArgs(DiagnosticOptions &Opts, ArgList &Args,
   } else if (Args.hasArg(OPT_print_diagnostic_groups)) {
     Opts.PrintDiagnosticNames = PrintDiagnosticNamesMode::Group;
   }
-  Opts.PrintEducationalNotes |= Args.hasArg(OPT_print_educational_notes);
   if (Arg *A = Args.getLastArg(OPT_diagnostic_documentation_path)) {
     Opts.DiagnosticDocumentationPath = A->getValue();
   }