Type names should not be quoted

Our actual convention, contrary to what I said in 59a2111b23, is not to
quote type names, as evidenced by unquoted use of format_type_be()
result value in error messages.  Remove quotes from recently tweaked
messages accordingly.

Per note from Tom Lane

src/backend/commands/trigger.c

@@ -438,7 +438,7 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-					 errmsg("function %s must return type \"%s\"",
+					 errmsg("function %s must return type %s",
 							NameListToString(stmt->funcname), "trigger")));
 	}