Remove lib.es6.d.ts from the project

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The core type definitions have been reshuffled a bit so some ES6 definitions (Map for example) that were previously available when targeting ES5 with TypeScript 1.4 can no longer be resolved with
TypeScript 1.5.0-beta. This broke the NodeJS definitions, amongst other things (e.g. microsoft/TypeScript#2953), so as a temporary workaround I've included the ES6 type definitions (lib.es6.d.ts) that ship with TypeScript 1.5.0-beta in the project. This way the ES6 definitions in the project are used instead of the ES5 definitions that would otherwise be used by TypeScript when targeting ES5. If the TypeScript peeps fix this issue in a future release lib.es6.d.ts should be removed from the project.

es6-promise.d.ts was removed from the project in 0e822b4 because lib.es6.d.ts already contains a definition for Promise, which caused naming conflicts. If lib.es6.d.ts is removed from the project in the future then es6-promise.d.ts will need to be added back in.

[enlight]

Also relevant: microsoft/TypeScript#3215