Deprecate when Babili is stable

Let's make sure Babili passes all of our tests (and PR them if possible):

[x] async-hoisting - tests interaction with transform-async-to-generator; Babili passes but has no existing tests for multiple transforms interacting AFAICT
[x] conditional-expression - PR'd
[x] decorated-classes - the decorator transform is deprecated pending spec changes so this isn't very important
[x] destructuring - ensures that destructuring is not inlined across; Babili passes, not a particularly valuable test as it could be done, it just isn't
[x] exported / exported-anonymous-function - if this regresses everyone's code will break, so a test isn't super important
[x] if-statement-and-unreachable - covered
[x] if-statement - covered
[x] inlining-bailout - covered (and more tests further down)
[x] inlining-disabled - not relevant since it can't be disabled in Babili
[x] inlining - definitely covered (and more above)
[x] logical-expression - this is the entire point of guarded-expressions
[ ] node-env-inline - appears to fail without passPerPreset; can be fixed by making it run at Program:exit but this slightly regresses output size (unless mangle is also moved to Program:exit), and crashes on the React test case npm run build && node ./scripts/benchmark.js ./scripts/fixtures/backbone.js && node ./scripts/benchmark.js ./scripts/fixtures/react.js && node ./scripts/benchmark.js ./scripts/fixtures/jquery.js
[x] regression-10 - removing the only statement from a shorthand if shouldn't break the AST; covered
[x] regression-16 - using multiple indeterminate identifiers in a condition shouldn't cause a false positive; covered by babel-traverse test
[x] regression-7 - assignments to unused vars in child scopes should also be eliminated; would require an upstream regression in how bindings are created
[x] unreachable - covered
[x] unused-classes - no test but it works and is not very important (how often do you declare a class that isn't used?)
[x] unused-functions - same as above
[x] unused-vars - covered

erikdesjardins / babel-plugin-transform-dead-code-elimination

Deprecate when Babili is stable #22