Anim: remove Slotted Actions experimental flag from prefs in non-exp build

Remove the 'Slotted Actions' (`use_animation_baklava`) experimental flag
from the preferences RNA, in non-experimental builds.

The experimental flag is already zeroed out when loading the
preferences. This commit ensures that it stays zeroed out. The rest of
the code assumes that the flag is always `false` in non-experimental
builds.

Pull Request: https://projects.blender.org/blender/blender/pulls/128483

source/blender/makesrna/intern/rna_userdef.cc

@@ -7583,6 +7583,8 @@ static void rna_def_userdef_experimental(BlenderRNA *brna)
                            "work around invalid usercount handling in code that may lead to loss "
                            "of data due to wrongly detected unused data-blocks");
 
+#  ifdef WITH_ANIM_BAKLAVA
+  /* Only allow setting this to 'true' when actually built with Baklava. */
   prop = RNA_def_property(srna, "use_animation_baklava", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, nullptr, "use_animation_baklava", 1);
   RNA_def_property_ui_text(
@@ -7590,6 +7592,7 @@ static void rna_def_userdef_experimental(BlenderRNA *brna)
       "Multi-Slot Actions",
       "The new 'layered' Action can contain the animation for multiple data-blocks at once");
   RNA_def_property_update(prop, 0, "rna_userdef_update");
+#  endif
 }
 
 static void rna_def_userdef_addon_collection(BlenderRNA *brna, PropertyRNA *cprop)