remove unused method

Author: rmorshea

src/idom/core/_thread_local.py

@@ -20,6 +20,3 @@ def get(self) -> _StateType:
         else:
             state = self._state[thread]
         return state
-
-    def set(self, state: _StateType) -> None:
-        self._state[current_thread()] = state