Fix superfluous triple-slash declarations

[machty]

Attempt to fix #564

Currently running into issues with jscodeshift/babel failing to parse export const foo = ... in .d.ts files in declaration.

cc @NullVoxPopuli

[NullVoxPopuli]

I was able to easily reproduce the issue you mentioned in discord in the test suite.

Here is what the tests look like to see how to test this sort of stuff NullVoxPopuli/fix-bad-declaration-output#10

it seems this is the issue: facebook/jscodeshift#539

[NullVoxPopuli]

after some more digging, it seems the types are wrong -- how are they generated?

a d.ts file should have declare if a const is not going to have an initializer.