Revert "report_errors with expected failures (#51)"

This reverts commit 02041f6c9f and
https://github.com/boostorg/core/pull/51.

Reason for revert: The change allows for incorrect result code returned
from the process if the number of failures is a multiple of 256. This
may result in test failures being taken as success by the parent process.

include/boost/core/lightweight_test.hpp

@@ -383,13 +383,14 @@ inline int report_errors()
     {
         BOOST_LIGHTWEIGHT_TEST_OSTREAM
           << "No errors detected." << std::endl;
+        return 0;
     }
     else
     {
         BOOST_LIGHTWEIGHT_TEST_OSTREAM
           << errors << " error" << (errors == 1? "": "s") << " detected." << std::endl;
+        return 1;
     }
-    return errors;
 }
 
 } // namespace boost