Unnecessary __default

[Rich-Harris]

Most of the time, this...

var foo = require('foo');
var foo__default = ('default' in foo ? foo['default'] : foo);

foo__default();

...is unnecessary. If we're only using the default import (as is always the case in non-strict mode, by definition, and often the case in strict mode), then we don't need the original foo reference. So the code could be written more neatly:

var foo = require('foo');
foo = ('default' in foo ? foo['default'] : foo);

foo();

It's only on the rare occasions that we import both default and named bindings from external modules that we need to do the __default dance.