Remove internal frames from SyntaxErrors

[gilch]

Displaying the inner workings of the compiler just adds noise for the end user.

[gilch]

The REPL already does this, but you can still see the traceback for SyntaxErrors when running a main module, and maybe when compiling one.

[brandonwillard]

I looked into this a while back, and it was a pretty tricky thing to do well.

[gilch]

The way the REPL suppresses these makes them incompatible with doctests. It's easy enough to work around, but not ideal.