Remove incorrect types to reduce maintenance overhead

[DerZade]

This PR removes the typescript type declarations.

As already mentioned in #342, #392 and #364, the types shipped with this package are plain incorrect. This is an issue every developer has to work around when using this package together with typescript.

I can tell that this package is basically abandoned, so I decided to remove the index.d.ts instead of patching it as #364 did.
This ensures minimal maintenance effort, while allowing other motivated developers to publish correct types in @types/flexsearch.

@ts-thomas Please take five minutes to merge and publish this so that hundreds (or even thousands) of developers do not have to invest five minutes each to work around this every time they want to install this package. (As a small incentive 🙈 I even sponsored you for this)

Thank you for the amazing package!

[ts-thomas]

Thanks a lot. The whole type definition thing was a desaster. My intention was that this specific part could be managed by the community, but we couldn't archive this goal. I will add a proper type definition soon like I made in the Mikado project.