repl: don’t complete expressions when eval fails

Instead of changing the way “simple” expressions are detected,
switch to ignoring errors when completing. This approach is more
generic than the previous one from 0b66b8f2, but also changes
the way errors are thrown when completing.

This reverts the code changes from commit 0b66b8f2.
The test case is left intact.

Fixes: https://github.com/nodejs/node/issues/6325
PR-URL: https://github.com/nodejs/node/pull/6328


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>