Remove bare array creation from multi assign

[RX14]

Previously, a = 1, 2, 3 was parsed as a = [1, 2, 3]. This is a weird special case with strange side-effects such as a = 1, b = 2 being parsed as a = [1, b = 2] which is... not optimal. The previous statement can happen easily as a syntax error:

a = 1,
b = 2

This doesn't effect swapping expressions (a, foo.bar = foo.bar, 2) or destructuring (a, b, c = method()).

[ysbaddaden]

I agree. This is too much sugar.