Cleanup: move bl_description to doc-strings

This is already done almost everywhere, prefer doc-strings unless
there is a reason for the tool-tip and Python doc-string to differ.

scripts/startup/bl_operators/anim.py

@@ -525,16 +525,11 @@ class ARMATURE_OT_copy_bone_color_to_selected(Operator):
 
 
 class ARMATURE_OT_collection_solo_visibility(Operator):
-    """Hide all other bone collections and show the active one.
-
-    Note that it is necessary to also show the ancestors of the active bone
-    collection in order to ensure its visibility.
-    """
+    """Hide all other bone collections and show the active one. """ \
+        """Note that it is necessary to also show the ancestors of the active """ \
+        """bone collection in order to ensure its visibility"""
     bl_idname = "armature.collection_solo_visibility"
     bl_label = "Solo Visibility"
-    bl_description = "Hide all other bone collections and show the active one. " + \
-        "Note that it is necessary to also show the ancestors of the active " + \
-        "bone collection in order to ensure its visibility"
     bl_options = {'REGISTER', 'UNDO'}
 
     name: StringProperty(name='Bone Collection')
@@ -589,11 +584,11 @@ class ARMATURE_OT_collection_show_all(Operator):
 
 
 class ARMATURE_OT_collection_remove_unused(Operator):
-    """Remove all bone collections that have neither bones nor children."""
+    """Remove all bone collections that have neither bones nor children.\n""" \
+        """This is done recursively, so bone collections that only have unused children are also removed"""
+
     bl_idname = "armature.collection_remove_unused"
     bl_label = "Remove Unused Bone Collections"
-    bl_description = ("Remove all bone collections that have neither bones nor children.\n"
-                      "This is done recursively, so bone collections that only have unused children are also removed")
     bl_options = {'REGISTER', 'UNDO'}
 
     @classmethod