actor: only remove control effects of given animations in unloadAnims

The previous behavior was for unloadAnims() to remove the control effects from all animations, even when only one animation was passed in, which is unintuitive behavior.

Fixes #853

direct/src/actor/Actor.py

@@ -2281,7 +2281,7 @@ class Actor(DirectObject, NodePath):
                             # our handle on them go. This is especially
                             # important if the anim control was blending
                             # animations.
-                            animDef.animControl.getPart().clearControlEffects()
+                            animDef.animControl.getPart().setControlEffect(animDef.animControl, 0.0)
                             animDef.animControl = None