Delete merge.js

[ExplodingCabbage]

Reasons:

• This has been badly broken for as long as it has existed (see 3-way merge #181 (comment), Incorrect merge #341)
• I have no plans to fix it, in part because it's unclear what it's even supposed to do (see 3-way merge #181 (comment))
• With the introduction of types (TypeScript rewrite #591, Please ship TypeScript definitions #303), just leaving this around untouched becomes awkward. I need to decide whether to port this stuff to TypeScript or simply cull it. And I'd rather cull it, because it's broken and anyone who tries to use it is probably just unwittingly introducing bugs into their code.