feat(core): drop support for after-step-hook

This was necessary for hooking display.refresh() with the old UI toolkit.
With the new one, we explicitly refresh the display after every paint, so
implicit after-step refresh seems no longer necessary.

core/.changelog.d/3633.changed

@@ -0,0 +1 @@
+Improved device responsiveness by removing unnecessary screen refreshes.

core/src/trezor/loop.py

@@ -20,9 +20,6 @@ if TYPE_CHECKING:
     AwaitableTask = Task | Awaitable
     Finalizer = Callable[[Task, Any], None]
 
-# function to call after every task step
-after_step_hook: Callable[[], None] | None = None
-
 # tasks scheduled for execution in the future
 _queue = utimeq.utimeq(64)
 
@@ -179,8 +176,6 @@ def _step(task: Task, value: Any) -> None:
         else:
             if __debug__:
                 log.error(__name__, "unknown syscall: %s", result)
-        if after_step_hook:
-            after_step_hook()
 
 
 class Syscall:

core/src/trezor/ui/__init__.py

@@ -60,11 +60,6 @@ else:
     refresh = display.refresh
 
 
-# in both debug and production, emulator needs to draw the screen explicitly
-if utils.EMULATOR or utils.INTERNAL_MODEL == "T2B1" or utils.INTERNAL_MODEL == "T3B1":
-    loop.after_step_hook = refresh
-
-
 async def _alert(count: int) -> None:
     short_sleep = loop.sleep(20)
     long_sleep = loop.sleep(80)