Context don't have to be passed in setState method

Currently `setState` method (that is run from context object) have a first argument of context. This context is the same object for which we run this method, so in this method it could be accessed by `this` pointer. Using this method with different context than for which it is executed will be invalid, so it is also a bug.

Locate the setState declaration and implementation, then inspect its callers to confirm how the context argument is currently passed. Update the API consistently and verify that existing usage still compiles and uses the owning context; the issue is done when the redundant argument is no longer required.

Written by the indexing model from the issue text.