As types are no longer used in index requests, we can remove the type parameter
from `prepareIndex` methods in the `Client` interface. However, just changing the signature
of `prepareIndex(index, type, id)` to `prepareIndex(index, id)` risks confusion when
upgrading with the previous (now removed) `prepareIndex(index, type)` method -
just changing the dependency version of java code would end up silently changing the
semantics of the method call. Instead we should just remove this method entirely, and
replace it by calling `prepareIndex(index).setId(id)`