Remove the Execute.discover setter dead code

tmt/steps/execute/__init__.py

@@ -34,7 +34,7 @@
 from tmt.steps.context.reboot import RebootContext
 from tmt.steps.context.restart import RestartContext
 from tmt.steps.context.restraint import RestraintContext
-from tmt.steps.discover import Discover, DiscoverPlugin, DiscoverStepData
+from tmt.steps.discover import Discover, DiscoverPlugin
 from tmt.utils import (
     Command,
     CommandOutput,
@@ -54,6 +54,7 @@
     import tmt.base.plan
     import tmt.result
     import tmt.steps.discover
+    from tmt.steps.discover.fmf import DiscoverFmf
 
 # Test data and checks directory names
 TEST_DATA = 'data'
@@ -694,18 +695,19 @@ def go(
         logger.verbose('exit-first', self.data.exit_first, 'green', level=2)
 
     @property
-    def discover(self) -> Discover:
+    def discover(self) -> Union[Discover, 'DiscoverFmf']:
         """
-        Return discover plugin instance
+        Return discover step or discover plugin instance
+
+        This is used for iterating over discovered tests and setting the
+        workdir. During the upgrade phase of the upgrade plugin it
+        returns instance of DiscoverFmf with upgrade tasks.
+
+        FIXME: Find a way how to handle this more cleanly.
         """
-        # This is necessary so that upgrade plugin can inject a fake discover
 
         return self.step.plan.discover
 
-    @discover.setter
-    def discover(self, plugin: Optional[DiscoverPlugin[DiscoverStepData]]) -> None:
-        self._discover = plugin
-
     def prepare_tests(self, guest: Guest, logger: tmt.log.Logger) -> list[TestInvocation]:
         """
         Prepare discovered tests for testing

tmt/steps/execute/upgrade.py

@@ -236,21 +236,19 @@ def __init__(self, **kwargs: Any) -> None:
         super().__init__(**kwargs)
         self._discover_upgrade: Optional[DiscoverFmf] = None
 
-    @property  # type:ignore[override]
+    @property
     def discover(self) -> Union[Discover, DiscoverFmf]:
         """
-        Return discover plugin instance
+        Return discover step or discover plugin instance
+
+        If we are in the second phase (upgrade), take tests from our
+        fake discover plugin.
         """
 
-        # If we are in the second phase (upgrade), take tests from our fake
-        # discover plugin.
         if self._discover_upgrade:
             return self._discover_upgrade
-        return self.step.plan.discover
 
-    @discover.setter
-    def discover(self, plugin: Optional[DiscoverPlugin[DiscoverStepData]]) -> None:
-        self._discover = plugin
+        return self.step.plan.discover
 
     @property
     def tasks(