Fix DCE for ArrayPatterns and ObjectPatterns

[boopathi]

• Bail out for replacement of single use variable inside a function

TODO (for later): maybe a more intelligent approach to replace - for ex,

// from
const [a] = b; return a;
const {a} = b; return a;

// to
return b[0];
return b.a;

• (Close Incorrect behaviour with array destructuring #151)

[loganfsmyth]

const [a] = b; return a; isn't the same as b[0];, that'll break for Map and Set and such.

[boopathi]

Yeah! Forgot about those. Thanks.

[boopathi]

I think this PR is good to go to fix the bug. Will investigate later what other transformations can be applied.